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The field of phylogenetics employs a variety of methods and techniques to study the evolution of life across the planet. Understanding evolutionary relationships is crucial to enriching our understanding of how genes and organisms have evolved throughout time and how they could possibly evolve in the future. Eucopia sculpticauda Faxon, 1893 is a deep-water peracarid in the order Lophogastrida Boas, 1883, which can often be found in high abundances in pelagic trawls. The species can be found along the Mariana Trench, in the Mid-Atlantic Ridge, west Atlantic and east Pacific Oceans, and in the Gulf of Mexico and as deep as 7526 m. Recent collections of E. sculpticauda in the Gulf of Mexico have revealed putative cryptic diversity within the species based on both molecular and morphological evidence. Previous studies have documented two different morphotypes of the telson: the terminal part of the pleon (abdomen) and part of the tail fan. In adults, the morphotypes can be distinguished by lateral constrictions in the telson. This evidence, combined with a previous barcoding study, led to the speculation that telson morphology may be a distinguishing character useful to define cryptic diversity within E. sculpticauda. This study presents additional molecular data from the mitochondrial genes cytochrome c oxidase subunit I, and the large ribosomal subunit (16S), and the nuclear histone 3 gene (H3) to investigate telson morphotypes in relation to evolutionary history within this species. Molecular data identified two strongly supported clades, lending support for potential cryptic diversification within the Gulf of Mexico. Investigations into telson morphology suggest that this character may be informative, but the morphotypes were sometimes ambiguous and additional characters could not be found that discriminate clades. At present, our data suggest early evidence for cryptic diversification within Gulf of Mexico populations, but additional morphological characters and geographic sampling are needed before a new species can be described., (© The Author(s) 2024. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology.)

Due to their distinctive anatomical characteristics, land slugs are appealing research subjects from a variety of angles, including stem cell biology, regeneration, embryonic development, allometry, and neurophysiology. Here we present SlugAtlas, an anatomical and histological online resource of the land slugs Deroceras laeve and Ambigolimax valentianus. The atlas is composed of series of histological sections on the horizontal, sagittal, and transversal planes for both species with 3D viewing tools of their major organs. The atlas was used in this work for a comparative analysis of the major organs and tissues of these two species. We provide a comprehensive histological description of them and an explanation of novel findings of unique features of their anatomy. For D. laeve, we additionally studied its ability for degrowth and regrowth, a feature that characterizes animals with high regeneration potential and obtained initial results on the study of the regeneration of its tail. SlugAtlas is a resource that is also built to accommodate future growth and, along with the experimental techniques that we have developed, will provide the foundation for research projects in a variety of biological domains., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2024 Lozano-Flores et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

Nudibranchs, with their mesmerizing diversity and ecological significance, play crucial roles in marine ecosystems. Central to their feeding prowess is the radula, a chitinous structure with diverse morphologies adapted to prey preferences and feeding strategies. This study focuses on elucidating wear coping mechanisms in radular teeth of carnivorous molluscs, employing Dendronotus lacteus (Dendronotidae) and Flabellina affinis (Flabellinidae) as model species. Both species forage on hydrozoans. Through scanning electron microscopy, confocal laser scanning microscopy, nanoindentation, and energy-dispersive X-ray spectroscopy, the biomechanical and compositional properties of their teeth were analyzed. Notably, tooth coatings, composed of calcium (Ca) or silicon (Si) and high hardness and stiffness compared to the internal tooth structure, with varying mineral contents across tooth regions and ontogenetic zones, were found. The presence of the hard and stiff tooth coatings highlight their role in enhancing wear resistance. The heterogeneities in the autofluorescence patterns related to the distribution of Ca and Si of the coatings. Overall, this study provides into the biomechanical adaptations of nudibranch radular teeth, shedding light on the intricate interplay between tooth structure, elemental composition, and ecological function in marine molluscs., (© 2024 The Author(s). Journal of Morphology published by Wiley Periodicals LLC.)

The Miocene Climate Optimum (MCO, ~ 17-14 Ma) was a time of extraordinary marine biodiversity in the Circum-Mediterranean Region. This boom is best recorded in the deposits of the vanished Central Paratethys Sea, which covered large parts of central to southeastern Europe. This sea harbored an extraordinary tropical to subtropical biotic diversity. Here, we present a georeferenced dataset of 859 gastropod species and discuss geodynamics and climate as the main drivers to explain the changes in diversity. The tectonic reorganization around the Early/Middle Miocene boundary resulted in the formation of an archipelago-like landscape and favorable conditions of the MCO allowed the establishment of coral reefs. Both factors increased habitat heterogeneity, which boosted species richness. The subsequent cooling during the Middle Miocene Climate Transition (~ 14-13 Ma) caused a drastic decline in biodiversity of about 67%. Among the most severely hit groups were corallivorous gastropods, reflecting the loss of coral reefs. Deep-water faunas experienced a loss by 57% of the species due to changing patterns in circulation. The low sea level led to a biogeographic fragmentation reflected in higher turnover rates. The largest turnover occurred with the onset of the Sarmatian when bottom water dysoxia eradicated the deep-water fauna whilst surface waters-dwelling planktotrophic species underwent a crisis., (© 2024. The Author(s).)

Molluscs have undergone many transitions between separate sexes and hermaphroditism, which is of interest in studying the evolution of sex determination and differentiation. Here, we combined multi-locus genotypes obtained from restriction site-associated DNA (RAD) sequencing with anatomical observations of the gonads of three deep-sea hydrothermal vent gastropods of the genus Alviniconcha living in the southwest Pacific. We found that all three species (Alviniconcha boucheti, Alviniconcha strummeri, and Alviniconcha kojimai) share the same male-heterogametic XY sex-determination system but that the gonads of XX A. kojimai individuals are invaded by a variable proportion of male reproductive tissue. The identification of Y-specific RAD loci (found only in A. boucheti) and the phylogenetic analysis of three sex-linked loci shared by all species suggested that X-Y recombination has evolved differently within each species. This situation of three species showing variation in gonadal development around a common sex-determination system provides new insights into the reproductive mode of poorly known deep-sea species and opens up an opportunity to study the evolution of recombination suppression on sex chromosomes and its association with mixed or transitory sexual systems., (© The Author(s) 2024. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

Invasive non-native freshwater mollusks are a growing concern in South America, with 16 species already recorded in the region. Among them, Sinotaia quadrata has only been documented in Argentina, for the first time in the Punilla Valley, Córdoba (2009) and La Plata, Buenos Aires (since 2015). In this study, we report the presence of S. quadrata in two additional areas, the Río de la Plata River and a stream (unnamed) in the Paraná River basin, two of the most significant rivers in South America, located in the provinces of Buenos Aires and Entre Ríos, respectively. These new records confirm the invasive nature of this species, which has also been identified in Europe, the United States, and Africa in recent years. The findings of this study highlight the need for continued monitoring and management of invasive species in South America's freshwater ecosystems.

Few studies have considered the capabilities of gastropods living in minerally-deficient acidified coastal waters to compensate for outer shell corrosion or compromised growing edge shell production. We compared inner shell thickening between pristine shells (control) and corroded shells (experiment) of two related intertidal neritid gastropod species from reduced salinity and acidified environments. We predicted that the rocky-shore, Nerita chamaeleon, which has greater access to shell building biomineralization substrates, should better control shell thickness than the estuarine, Neripteron violaceum. Accordingly, N. chameleon was found to compensate perfectly for variation in the thickness of the outer calcitic blocky layer (BL). Optimal shell thickness (OST) was maintained by selective reabsorption of the aperture ridge of the distal shell (aragonitic crossed-lamellar layer, CL) and by increased internal deposition of proximal (older) shell (aragonitic protocrossed lamellar, PCL). Despite greater exposure to acidification and hyposalinity, N. violaceum showed no significant compensatory shell thickening. These findings reveal that shell thickening capability may vary greatly among intertidal gastropods and that this may be constrained by environmental biomineralization substrate availability. Such environmentally-related responses carry implications for predicted future reductions in coastal water pH and salinity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Understanding the underlying reasons for phenotypic plasticity and resulting morphological disparity is one of the key topics of evolutionary research. The phenotypic plasticity of extant and fossil melanopsids has been widely documented. Yet millennial-resolution, well-dated records from small aquatic habitats harboring endemics are scarce. The thermal spring-fed Lake Pețea is an ice age refugia harboring a unique endemic warm-water fauna. Subfossil melanopsids display incredible morphological variability from smooth to keeled, elongated to ribbed, shouldered forms. Numerous morphotypes have been considered as individual taxa with a fluent succession from the smooth elongated to the ribbed, shouldered types. This study presents an extensive morphometric analysis of subfossil melanopsids (ca. 3500 specimens) derived from stratified samples with an independent chronology. The aim was to separate morphotypes for investigations of temporal morphological disparity. Our results challenge the widely accepted hypothesis that proposes the evolution of shouldered, compressed, ribbed shells through a two-step process from smooth elongated spindle-shaped shells. Instead, it suggests that the subfossil shells belong to two distinct taxa present throughout the available stratigraphic data. The main components of shape variation, shape globularity, and shell coiling seem allometry-related. Ribs, striation, and keels appear randomly. High-spired spindle-shaped forms were considered to represent specimens of Microcolpia daudebartii hazayi. Bulkier low-spired and shouldered specimens represent phenotypes of Mi. parreyssii parreyssii. The collective and random distribution of morphotypes from the early stages of the lake's history also refutes the idea of a continuous transformation of the elongated forms into compressed, shouldered ones. Rather points to multiple events and environmental stimuli triggering development. Melanopsids appear in Late Glacial horizons, with Theodoxus prevostianus preferring temperatures above 23°C which may indicate the subordinate presence of hot water microhabitats in cooler waters., (© 2024 Wiley Periodicals LLC.)

The Mediterranean region is a biodiversity hotspot. Mollusks represent the second most diverse phylum, with high species richness, endemism, and significant numbers of threatened species. The non-marine species are an especially vulnerable group. New taxa are frequently described although the descriptions often lack biological support. This is true for Helicella candoni Thach, 2018, originally described from Puerto de Santa María, Cádiz, Spain. Thatch (2018) considered H. candoni to be similar to Xerotricha madritensis (Rambur, 1868) but the comparison was made on the basis of basic conchological characters. The present study analyzed topotypes of X. madritensis and H. candoni using integrative taxonomy to evaluate the relationship of the two taxa and their status within Helicella A. Férussac, 1821 and Xerotricha Monterosato, 1892 respectively. A matrix of the mitochondrial cytochrome c oxidase subunit I (COI) yielded a total of 618 bp. Bayesian and Maximum Likelihood analyses showed that H. candoni and X. madritensis clustered closely together along with Helicella itala. Mean sequence divergence for COI between H. candoni and X. madritensis was 1.42 %. Both taxa are similar in shell shape and colour. Genitalia dimensions of H. condoni were very similar to those of X. madritensis. These data indicate that H. candoni is a junior synonym of X. madritensis. The phylogenetic analyses showed that, despite its morphological similarities, X. madritensis is a species of Helicella instead of Xerotricha., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier GmbH.)

The freshwater slugs of the genus Acochlidium (Heterobranchia, Gastropoda, and Acochlidimorpha) are peculiar, one to two centimeter sized animals found only in small coastal rivers and streams of Southeast Asian and Western Pacific islands. When first described by Bücking, the author observed a branching "net of dendritic vessels connected to the heart," which he assumed to have replaced the original gastropod gill. In the present study, we compare the renopericardial systems of four Acochlidium species in microanatomical, histological and ultrastructural detail and identify where exactly the enigmatic, subepidermal "dorsal vessels" connect to the renopericardial system to examine if they can really function as a gill. Acochlidium have elaborate renopericardial systems compared to their ancestrally marine and also freshwater relatives. The primary site of ultrafiltration is the epicardium of the atrium with podocytes as usual for gastropods. The "dorsal vessels" in Acochlidium are extensions of the outer epithelium of the pericardial cavity and represent true vessels, that is, coelomatic channels, having an endothelium with podocytes. Hence, they considerably enlarge the site of ultrafiltration increasing the pericardial surface. "Dorsal vessels" in Acochlidium are therefore not homologous to externally similar morphological structures in Sacoglossa (marine panpulmonate slugs and snails). The multiplication of renopericardioducts in Acochlidium is a unique feature within Mollusca that enhances the negative pressure necessary for ultrafiltration in the thin, tube-like dorsal vessels and as a consequence the transport of primary urine from the pericardium to the kidney. The circulatory and excretory systems in Acochlidium are adaptations to a lifestyle in their freshwater environment in which snail bodies are hyposmotic and accrue considerable influx of surplus water into the body, which needs to be expelled., (© 2023 The Authors. Journal of Morphology published by Wiley Periodicals LLC.)

A new species of Hua , Hua qiannanensis sp. nov., is described from Guizhou Province, China, based on morphological and molecular evidence. The new species can be distinguished from its congeners by the following combination of characters: the smooth shell, only three smaller cusps of lateral teeth on the inner side, outer marginal teeth with eight flattened and rounded denticles, an ovipositor pore in females, and BW/H ≥ 80%, B/H = 76.8-82.3%. Molecular analysis based on partial mitochondrial COI and 16S rDNA also supports the systematic position of the new taxon.

Gastropods of the superfamily Conoidea are present in high diversity in the oceans and are characterized by having modified foregut anatomy and radular morphology. This study provides details on variations in the radula teeth of the species Hastula cinerea, which have hypodermic radula teeth of the toxoglossan type and are part of the Terebridae family - inserted in the Conoidea superfamily. Hastula cinerea specimens were collected at Flecheiras beach, Trairi, Ceará, Brazil. Scanning Electron Microscopy (SEM) was performed to analyse the radula specificities. Thirty specimens were used between females and males, with different sizes. The total length of the shell and the length of the teeth of all analysed specimens were measured. With the SEM result, more than one radula tooth morphotype was found for the species H. cinerea. The pattern of the teeth found is similar to the hypodermic teeth of the group, however, with structural and length differences between smaller and larger individuals. It was possible to observe three radula variations (morphotype-1, morphotype-2 and morphotype-3), 26 related to different sizes of individuals, regardless of sex, configuring a variation in the radula teeth. Therefore, this result brings a contribution that stimulates future research with the functional morphology of H. cinerea and others auger snails., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier GmbH. All rights reserved.)

Nudibranchia is the order of Gastropoda, which is known for its high diversity of dietary specializations and a diversified morphology of the buccal armature. The characters of the buccal armature are adaptive to the feeding mechanisms and diet preferences, but they also are phylogenetically informative. The morphological differences in the buccal armature imply different mechanisms of the synthesis and morphology of the formation zones. Here, we report new data on the morphology of the buccal complex in a cladobranch species with broad radula, Dendronotus frondosus, using light microscopy, transmission and scanning elctron microscopy and computer-based three- dimensional reconstruction and compare them with those on other nudibranchs. We report the presence of protective chitinous spindles in the epithelia of the oral tube and esophagus, which suggests the presence of Cnidaria in the diet of the studied mollusc species. Similar to other Cladobranchia, the jaw plate of D. frondosus is synthesized by the layer of gnathoblasts located posteriorly in the epithelial fold. Near the zone of jaw synthesis, the gnathoblasts with concentric granular endoplasmic reticulum structures were found. This may indicate the turnover of gnathoblasts during the life of a specimen. Despite that D. frondosus has a broad radula, the zone of its synthesis does not split into two parts, unlike other molluscs with broad radulae. A single radular tooth is formed by a few cells, such as in other Nudibranchia. The number of odontoblasts per tooth in D. frondosus is not defined by a tooth size. At the same time, the linear dimensions of the cells secreting radular teeth depend on the size of the teeth synthesized by them., (© 2023 Wiley Periodicals LLC.)

Gastropoda is morphologically highly variable and broadly distributed group of mollusks. Due to the high morphological and functional diversity of the feeding apparatus gastropods follow a broad range of feeding strategies: from detritivory to highly specialized predation. The feeding apparatus includes the buccal armaments: jaw(s) and radula. The radula comprises a chitinous ribbon with teeth arranged in transverse and longitudinal rows. A unique characteristic of the radula is its continuous renewal during the entire life of a mollusk. The teeth and the membrane are continuously synthesized in the blind end of the radular sac and are shifted forward to the working zone, while the teeth harden and are mineralized on the way. Despite the similarity of the general mechanism of the radula formation in gastropods, some phylogenetically determined features can be identified in different phylogenetic lineages. These mainly concern shape, size, and number of the odontoblasts forming a single tooth. The radular morphology depends on the shape of the formation zone and the morphology of the subradular epithelium. The radula first appears at the pre- and posttorsional veliger stages as an invagination of the buccal epithelium of the larval anterior gut. The larval radular sac is lined with uniform undifferentiated cells. Each major phylogenetic lineage is characterized by a specific larval radula type. Thus, the docoglossan radula of Patellogastropoda is characterized by initially three and then five teeth in a transverse row. The larval rhipidoglossan radula has seven teeth in a row with differentiation into central, lateral, and marginal teeth and later is transformed into the adult radula morphology by the addition of lateral and especially marginal teeth. The taenioglossan radula of Caenogastropoda is nearly immediately formed in adult configuration with seven teeth in a row., (© 2022 Wiley Periodicals LLC.)

The molluscan phylum is the second specious animal group with its taxa feeding on a variety of food sources. This is enabled by the radula, a chitinous membrane with embedded teeth, one important autapomorphy. Between species, radulae can vary in their morphology, mechanical, and chemical properties. With regard to chemical composition, some taxa (Polyplacophora and Patellogastropoda) were studied extensively in the past decades, due to their specificity to incorporate high proportions of iron, calcium, and silicon. There is, however, a huge lack of knowledge about radular composition in other taxa. The work presented aims at shedding light on the chemistry by performing energy-dispersive X-ray spectroscopy analyses on 24 molluscan species, thereof two Polyplacophora, two Cephalopoda, and 20 Gastropoda, which was never done before in such a comprehensiveness. The elements and their proportions were documented for 1448 individual, mature teeth and hypotheses about potential biomineralization types were proposed. The presented work additionally comprises a detailed record on past studies about the chemical composition of molluscan teeth, which is an important basis for further investigation of the radular chemistry. The found disparity in elements detected, in their distribution and proportions highlights the diversity of evolutionary solutions, as it depicts multiple biomineralization types present within Mollusca., (© 2022. The Author(s).)

The rhipidoglossan radula, consisting of numerous teeth in each transverse row, is characteristic of phylogenetically distant groups of gastropods, including Vetigastropoda, Neritimorpha and 'lower' Heterobranchia. Previous studies have revealed the main patterns in the formation of the rhipidoglossan radula of vetigastropods, the main feature of which is the division of the formation zone into two horns, where marginal teeth are formed by a multilayered epithelium (odontoblasts). This work is devoted to the study of the formation of the rhipidoglossan radula of Nerita litterata using light and electron microscopy. The data obtained show that, despite the different external morphology of the radular sac of neritids and vetigastropods, the radular sac of N. litterata, like that of vetigastropods, is divided into two parts, in which the marginal teeth are similarly formed by odontoblasts located in more than one layer. It seems probable that this complex, three-dimensional structure of the formation zone is associated with a broad radula with numerous elongate marginal teeth and could be characteristic of other gastropods with this type of radula. Additional supporting rods located along the odontoblasts and consisting of vacuolated cells were first discovered in Nerita., (© 2022 Wiley Periodicals LLC.)

The genus Thuridilla Bergh, 1872 comprises mostly tropical sap-sucking sea slugs species with flamboyantly coloured forms. However, the potential for cryptic or pseudocryptic species masked by convergent or polymorphic colour patterns has not been tested using molecular characters. In this study, we sampled 20 of the 23 recognized worldwide species and performed the most comprehensive molecular phylogenetic analysis of the genus to date using a multi-locus approach combining two mitochondrial (cytochrome c oxidase subunit I, 16S rRNA) and two nuclear (Histone H3, 28S rRNA) genes using maximum likelihood, maximum-parsimony and Bayesian criteria. Three molecular species delimitation methods (ABGD, GMYC, bPTP) and the morphology of radular teeth were additionally used to aid in species delimitation. Our analyses supported 35 species within Thuridilla, of which more than one-third (13) are part of a single radiation here named the Thuridilla gracilis (Risbec, 1928) species-complex. This complex includes T. gracilis, T. splendens (Baba, 1949), T. bayeri (Er. Marcus, 1965), and T. ratna (Er. Marcus, 1965), plus nine additional undescribed species. All 13 species are distinguishable by radular characters, external morphology and their DNA. The detection of this radiation led diversity of Thuridilla to be underestimated by about 25% and provides a new comparative system for studying the role of colour patterns in marine diversification., (© The Willi Hennig Society 2021.)

Extracts of the mantle and viscera of the Indo-Pacific nudibranchs Goniobranchus aureopurpureus and Goniobranchus sp. 1 afforded 11 new diterpenoids ( 1 - 11 ), all of which possess a tetracyclic spongian-16-one scaffold with extensive oxidation at C-6, C-7, C-11, C-12, C-13, and/or C-20. The structures and relative configuration were investigated by NMR experiments, while X-ray crystallography provided the absolute configuration of 1 , including a 2' S configuration for the 2-methylbutanoate substituent located at C-7. Dissection of animal tissue revealed that the mantle and viscera tissues differed in their metabolite composition with diterpenes 1 - 11 present in the mantle tissue of the two nudibranch species.

The radula, a chitinous membrane with embedded tooth rows, is the molluscan autapomorphy for feeding. The morphologies, arrangements and mechanical properties of teeth can vary between taxa, which is usually interpreted as adaptation to food. In previous studies, we proposed about trophic and other functional specialisations in taenioglossan radulae from species of African paludomid gastropods. These were based on the analysis of shape, material properties, force-resistance, and the mechanical behaviour of teeth, when interacting with an obstacle. The latter was previously simulated for one species (Spekia zonata) by the finite-element-analysis (FEA) and, for more species, observed in experiments. In the here presented work we test the previous hypotheses by applying the FEA on 3D modelled radulae, with incorporated material properties, from three additional paludomid species. These species forage either on algae attached to rocks (Lavigeria grandis), covering sand (Cleopatra johnstoni), or attached to plant surface and covering sand (Bridouxia grandidieriana). Since the analysed radulae vary greatly in their general size (e.g. width) and size of teeth between species, we additionally aimed at relating the simulated stress and strain distributions with the tooth sizes by altering the force/volume. For this purpose, we also included S. zonata again in the present study. Our FEA results show that smaller radulae are more affected by stress and strain than larger ones, when each tooth is loaded with the same force. However, the results are not fully in congruence with results from the previous breaking stress experiments, indicating that besides the parameter size, more mechanisms leading to reduced stress/strain must be present in radulae., (© 2021. The Author(s).)

The gastropod infraclass Euthyneura comprises at least 30,000 species of snails and slugs, including nudibranch sea slugs, sea hares and garden snails, that flourish in various environments on earth. A unique morphological feature of Euthyneura is the presence of two pairs of sensory head tentacles with different shapes and functions: the anterior labial tentacles and the posterior rhinophores or eyestalks. Here we combine molecular phylogenetic and microanatomical evidence that suggests the two pairs of head tentacles have originated by splitting of the original single tentacle pair (with two parallel nerve cords in each tentacle) as seen in many other gastropods. Minute deep-sea snails of Tjaernoeia and Parvaplustrum, which in our phylogeny belonged to the euthyneurans' sister group (new infraclass Mesoneura), have tentacles that are split along much of their lengths but associated nerves and epidermal sense organs are not as specialized as in Euthyneura. We suggest that further elaboration of cephalic sense organs in Euthyneura closely coincided with their ecological radiation and drastic modification of body plans. The monotypic family Parvaplustridae nov., superfamily Tjaernoeioidea nov. (Tjaernoeiidae + Parvaplustridae), and new major clade Tetratentaculata nov. (Mesoneura nov. + Euthyneura) are also proposed based on their phylogenetic relationships and shared morphological traits., (© 2021. The Author(s).)

Here, we report for the first time the snail intermediate host for the Amphimerus liver fluke, a foodborne trematodiasis. In Ecuador, Amphimerus of the Opisthorchiidae family, infects humans, cats, and dogs, in the tropical Pacific-coast region. Opisthorchiidae comprising also Clonorchis sinensis, Opisthorchis sp., and Metorchis sp., have complex life cycles involving a definitive and two intermediate hosts. We identified morphologically and investigated the presence and prevalence of Amphimerus cercaria and DNA in freshwater snails collected in a human-amphimeriasis endemic region in Ecuador, extracted DNA from snail tissue and emerged cercariae, performed real-time polymerase chain reaction (PCR) with the newly developed primers and probe amplifying the Amphimerus ribosomal internal transcribed spacer 2 (ITS2) region, and sequenced the amplified DNA fragment. We collected 2,800 snails, characterized four species Aroapyrgus sp., Melanoides tuberculata, Biomphalaria cousini, and Aplexa marmorata, isolated three cercariae morphotypes. Of the 640 snails analyzed by qPCR, only Aroapyrgus and one of the three cercariae resulted positive, at a 15% infection prevalence. Polymerase chain reaction revealed that the Aroapyrgus snail and cercaria-morphotype-3 corresponded to Amphimerus, but not to C. sinensis, Fasciola hepatica, or Paragonimus mexicanus. The sequence of amplified DNA product matched that of human-isolated Amphimerus. This finding constitutes the first documentation that Aroapyrgus sp. is the first intermediate host for the Amphimerus sp. that infect humans in Ecuador. The ITS2-gene PCR and sequencing analysis demonstrated a high prevalence of snail infection and proved useful for detecting the infection in snails, which findings can help the establishment of suitable control programs against transmission in any endemic region of interest.

Biological tissues may exhibit graded heterogeneities in structure and mechanical properties that are crucial to their function. One biological structure that shows variation in both structure and function is the molluscan radula: the organ comprises a chitinous membrane with embedded teeth and serves to process and gather food. The tooth morphologies had been well studied in the last decades, but the mechanical properties of the teeth are not known for the vast majority of molluscs. This knowledge gap restricts our understanding of how the radula is able to act effectively on a target surface whilst simultaneously resisting structural failure. Here we employed nanoindentation technique to measure mechanical properties (hardness and Young's modulus) on distinct localities of individual radular teeth from 24 species of African paludomid gastropods. These species have distinct ecological niches as they forage on algae on different feeding substrates. A gradual distribution of measured properties along the teeth was found in species foraging on solid or mixed feeding substrates, but soft substrate feeders exhibit teeth almost homogeneous in their biomechanical properties. The presence or absence of large-scale gradients in these taenioglossan teeth could directly be linked with their specific function and in general with the species ecology, whereas the radular tooth morphologies do not always and fully reflect ecology. STATEMENT OF SIGNIFICANCE: African Lake Tanganyika is well known for harbouring endemic and morphologically distinct genera. Its paludomid gastropods form a flock of high interest because of its diversity. As they show distinct radular tooth morphologies hypotheses about potential trophic specializations had always been at hand. Here we evaluated the mechanical properties Young's modulus and hardness of 9027 individual teeth from 24 species along the tooth by nanoindentation and related them with the gastropods' specific feeding substrate. We find that hard substrate feeders have teeth that are hard at the tips but much less stiff at the base and thus heterogeneous with respect to material properties, whereas soft substrate feeders have teeth that are flexible and homogenous with respect to material properties., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

Species identification is a key procedure for broad-scoped ecological, phylogeographic and evolutionary studies. However, to perform a taxonomic study in the molecular era is a complicated task that has many pitfalls. In the present study we use particular examples of common but difficult to distinguish European species within the genus of Polycera (Nudibranchia, Mollusca) to discuss the general issues of the "cryptic species" problem that has broad biological and interdisciplinary importance and can significantly impede ecological, evolutionary, and other biodiversity-related research. The largest dataset of molecular and morphological information for European nudibranchs ever applied encompasses a wide geographical area and shapes a robust framework in this study. Four species are recognized in the species complex, including a new one. It is shown that a lack of appropriate taxonomic analysis led recently to considerable errors in species identity assessment of this complex. Chromatic polymorphism for each species is mapped in a periodic-like framework and combined with statistical analysis of the diagnostic features that considerably facilitates identification of particular species in the complex for biologists and practitioners. The present study evidently shows that "cryptic" and "non-cryptic" components are present within the same species. Therefore, this species complex is well suited for the exploring and testing of general biological problems. One of the main conclusions of this study is that division of biological diversity into "cryptic" and "non-cryptic" components is counterproductive. We propose that the central biological phenomenon of a species can instead be universally designated as multilevel organismal diversity thereby provide a practical set of methods for its investigation., (© 2021. The Author(s).)

Recent technical innovations are revealing surprising patterns in mollusc shell pigmentation, such as an unexpectedly modest role for melanins and rapid divergences in the mix of pigments used to achieve similar colour patterns. The elucidation of the molecular genetic basis of shell pigmentation has been slow, probably because of the high genome complexity of gastropods and bivalves. Recent work within the old field of evolutionary ecology of shell pigmentation allows a greater role for the analysis of large-geographic-scale patterns (sometimes employing citizen-science data), as well as experimental field studies. However, the field remains dominated by land snails as model organisms, while colour pattern evolution in marine gastropods and bivalves, particularly those not exposed to visual predators, remains mysterious., (Copyright © 2020 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Other than in animal models of human disease, little functional imaging has been performed in most of the animal world. The aim of this study was to explore the functional anatomy of the European round back slug (Arionidae) and leopard slug (Limacidae) and to establish an imaging protocol for comparative species study. Radionuclide images with single photon emission computed tomography (SPECT) and positron emission tomography (PET) were obtained after injections of standard clinical radiopharmaceuticals 99m technetium dicarboxypropane diphosphonate (bone scintigraphy), 99m technetium mercaptoacetyltriglycine (kidney function), 99m technetium diethylenetriaminepentaacetic acid (kidney function), 99m technetium pertechnetate (mediated by the sodium-iodide symporter), 99m technetium sestamibi (cardiac scintigraphy) or 18 F-fluoro-deoxyglucose (glucose metabolism) in combination with magnetic resonance imaging (MRI) and computed tomography (CT) for uptake anatomic definition. Images were compared with anatomic drawings for the Arionidae species. Additionally, organ uptake data was determined for a description of slug functional anatomy in comparison to human tracer biodistribution patterns identifying the heart, the open circulatory anatomy, calcified shell remnant, renal structure (nephridium), liver (digestive gland) and intestine. The results show the detailed functional anatomy of Arionidae and Limacidae, and describe an in vivo whole-body imaging procedure for invertebrate species.

The land snail Ellobium chinense (L. Pfeiffer, 1855) (Eupulmonata, Ellobiida, Ellobiidae), which inhabits the salt marshes along the coastal areas of northwestern Pacific, is an endangered species on the IUCN Red List. Over recent decades, the population size of E. chinense has consistently decreased due to environmental interference caused by natural disasters and human activities. Here, we provide the first assessment of the genetic diversity and population genetic structures of northwestern Pacific E. chinense. The results analyzed with COI and microsatellites revealed that E. chinense population exhibit metapopulation characteristics, retaining under the influence of the Kuroshio warm currents through expansion of the Late-Middle and Late Pleistocene. We also found four phylogenetic groups, regardless of geographical distributions, which were easily distinguishable by four unidirectional and stepwise adenine-to-guanine transitions in COI (sites 207-282-354-420: A-A-A-A, A-A-G-A, G-A-G-A, and G-G-G-G). Additionally, the four COI hotspots were robustly connected with a high degree of covariance between them. We discuss the role of these covariate guanines which link to form four consecutive G-quadruplexes, and their possible beneficial effects under positive selection pressure.

Continued sampling of the latest Eocene to earliest Oligocene Gries Ranch Formation in Lewis County, Washington State, has yielded new heterobranch microgastropod species. Orbitestella kieli sp. nov., is the third fossil species of this genus and family Orbitestellidae from western North America. Two new species of Ammonicera, A. rolani sp. nov. and A. danieli sp. nov., are together only the second fossil record of this genus and the family Omalogyridae from the northeastern Pacific Ocean. New specimens of two previously recorded species, O. palaiopacifica Squires Goedert and A. benhami Squires Goedert, from early Eocene rocks of the Crescent Formation provide new data regarding shell morphology. The fossil record of both Ammonicera and Orbitestella in western North America is restricted to early Eocene to earliest Oligocene age rocks in Washington State.

Marine heterobranch slugs of the order Runcinida comprise 61 species, most of which inhabit the Atlantic Ocean and are referred to the genus Runcina. The Runcinida of the Pacific Ocean have been much less studied to date: only 12 species, from the genera Metaruncina Baba, 1967, Rfemsia Chernyshev, 1999, Runcinida Burn, 1963, Runcinella Odhner, 1924, Pseudoilbia M. C. Miller Rudman, 1968, and Runcina Forbes [in Forbes and Hanley], 1851, have been described from the region. Metaruncina, Rfemsia, and Runcinida are found in the Pacific Ocean only (Baba 1954, 1967; Burn 1963; Gosliner 1991; Chernyshev 1998, 1999, 2005, 2006). The genus Metaruncina, endemic from the Pacific coast of Asia, includes two species: M. setoensis (Baba, 1954) and M. nhatrangensis Chernyshev, 2005. The latter is the only runcinid described from the coastal waters of the South China Sea, where it was found in the bays of Nha Trang and Van Phong (Chernyshev 2005). During subsequent expeditions to the coastal waters of Vietnam, this species was also recorded from off Tho Chu Island (09°19'N, 103°30'E) and off Nam Du Island (09°43' N, 104°23' E). However, in addition to this common species, an undescribed species of Metaruncina was collected. A description of this new species is provided in the present paper. Type material was deposited at the Museum of the A.V. Zhirmunsky National Scientific Center of Marine Biology FEB RAS, Vladivostok, Russia (MIMB).

The forces exerted by the animal's food processing structures can be important parameters when studying trophic specializations to specific food spectra. Even though molluscs represent the second largest animal phylum, exhibiting an incredible biodiversity accompanied by the establishment of distinct ecological niches including the foraging on a variety of ingesta types, only few studies focused on the biomechanical performance of their feeding organs. To lay a keystone for future research in this direction, we investigated the in vivo forces exerted by the molluscan food gathering and processing structure, the radula, for five stylommatophoran species (Gastropoda). The chosen species and individuals have a similar radular morphology and motion, but as they represent different body mass classes, we were enabled to relate the forces to body mass. Radular forces were measured along two axes using force transducers which allowed us to correlate forces with the distinct phases of radular motion. A radular force quotient, AFQ = mean Absolute Force/bodymass 0.67 , of 4.3 could be determined which can be used further for the prediction of forces generated in Gastropoda. Additionally, some specimens were dissected and the radular musculature mass as well as the radular mass and dimensions were documented. Our results depict the positive correlation between body mass, radular musculature mass, and exerted force. Additionally, it was clearly observed that the radular motion phases, exerting the highest forces during feeding, changed with regard to the ingesta size: all smaller gastropods rather approached the food by a horizontal, sawing-like radular motion leading to the consumption of rather small food particles, whereas larger gastropods rather pulled the ingesta in vertical direction by radula and jaw resulting in the tearing of larger pieces.

Marine biodiversity has been yielding promising novel bioproducts from venomous animals. Despite the auspices of conotoxins, which originated the paradigmatic painkiller Prialt, the biotechnological potential of gastropod venoms remains to be explored. Marine bioprospecting is expanding towards temperate species like the dogwhelk Nucella lapillus , which is suspected to secrete immobilizing agents through its salivary glands with a relaxing effect on the musculature of its preferential prey, Mytilus sp. This work focused on detecting, localizing, and testing the bioreactivity of cysteine-rich proteins and peptides, whose presence is a signature of animal venoms and poisons. The highest content of thiols was found in crude protein extracts from the digestive gland, which is associated with digestion, followed by the peribuccal mass, where the salivary glands are located. Conversely, the foot and siphon (which the gastropod uses for feeding) are not the main organs involved in toxin secretion. Ex vivo bioassays with Mytilus gill tissue disclosed the differential bioreactivity of crude protein extracts. Secretions from the digestive gland and peribuccal mass caused the most significant molecular damage, with evidence for the induction of apoptosis. These early findings indicate that salivary glands are a promising target for the extraction and characterization of bioactive cysteine-rich proteinaceous toxins from the species.

The radula is the food gathering and processing structure and one important autapomorphy of the Mollusca. It is composed of a chitinous membrane with small, embedded teeth representing the interface between the organism and its ingesta. In the past, various approaches aimed at connecting the tooth morphologies, which can be highly distinct even within single radulae, to their functionality. However, conclusions from the literature were mainly drawn from analyzing mounted radulae, even though the configuration of the radula during foraging is not necessarily the same as in mounted specimens. Thus, the truly interacting radular parts and teeth, including 3D architecture of this complex structure during foraging were not previously determined. Here we present an experimental approach on individuals of Vittina turrita (Neritidae, Gastropoda), which were fed with algae paste attached to different sandpaper types. By comparing these radulae to radulae from control group, sandpaper-induced tooth wear patterns were identified and both area and volume loss could be quantified. In addition to the exact contact area of each tooth, conclusions about the 3D position of teeth and radular bending during feeding motion could be drawn. Furthermore, hypotheses about specific tooth functions could be put forward. These feeding experiments under controlled conditions were introduced for stylommatophoran gastropods with isodont radulae and are now applied to heterodont and complex radulae, which may provide a good basis for future studies on radula functional morphology.

Pteropods, a group of holoplanktonic gastropods, are regarded as bioindicators of the effects of ocean acidification on open ocean ecosystems, because their thin aragonitic shells are susceptible to dissolution. While there have been recent efforts to address their capacity for physiological acclimation, it is also important to gain predictive understanding of their ability to adapt to future ocean conditions. However, little is known about the levels of genetic variation and large-scale population structuring of pteropods, key characteristics enabling local adaptation. We examined the spatial distribution of genetic diversity in the mitochondrial cytochrome c oxidase I (COI) and nuclear 28S gene fragments, as well as shell shape variation, across a latitudinal transect in the Atlantic Ocean (35°N-36°S) for the pteropod Limacina bulimoides. We observed high levels of genetic variability (COI π = 0.034, 28S π = 0.0021) and strong spatial structuring (COI Φ ST  = 0.230, 28S Φ ST  = 0.255) across this transect. Based on the congruence of mitochondrial and nuclear differentiation, as well as differences in shell shape, we identified a primary dispersal barrier in the southern Atlantic subtropical gyre (15-18°S). This barrier is maintained despite the presence of expatriates, a gyral current system, and in the absence of any distinct oceanographic gradients in this region, suggesting that reproductive isolation between these populations must be strong. A secondary dispersal barrier supported only by 28S pairwise Φ ST comparisons was identified in the equatorial upwelling region (between 15°N and 4°S), which is concordant with barriers observed in other zooplankton species. Both oceanic dispersal barriers were congruent with regions of low abundance reported for a similar basin-scale transect that was sampled 2 years later. Our finding supports the hypothesis that low abundance indicates areas of suboptimal habitat that result in barriers to gene flow in widely distributed zooplankton species. Such species may in fact consist of several populations or (sub)species that are adapted to local environmental conditions, limiting their potential for adaptive responses to ocean changes. Future analyses of genome-wide diversity in pteropods could provide further insight into the strength, formation and maintenance of oceanic dispersal barriers., (© 2020 The Authors. Journal of Evolutionary Biology published by John Wiley & Sons Ltd on behalf of European Society for Evolutionary Biology.)

Cephalaspidea is an order of marine gastropods found worldwide, often in sandy or muddy habitats, which has a convoluted taxonomic history based on convergent or ill-defined morphological characters. The cephalaspidean shell-which can be external and robust, internal, or altogether absent in the adult-is of particular interest in this group, and a well-resolved phylogeny can give us greater insight into the evolution of this character. Molecular data have clarified many relationships within Cephalaspidea, but studies involving few Sanger sequenced phylogenetic markers remain limited in the resolution they provide. Here we take a phylogenomic approach, the first to address internal cephalaspidean relationships, sequencing and assembling transcriptomes de novo from 22 ingroup taxa-representing the five currently accepted superfamilies, 10 of the 21 currently recognized families, and 21 genera-and analyzing these along with publicly available data. We generated two main datasets varying by a minimum taxon occupancy threshold (50% and 75%), and analyzed these using maximum likelihood, Bayesian inference and a coalescence-based method. We find a consistent, well-supported topology, with full support across most nodes including at the family and genus level, which also appears to be robust to the effect of compositional heterogeneity among amino acids in the dataset. Our analyses find Newnesioidea as the sister group to the rest of Cephalaspidea. Within the rest of the order, Philinoidea is the sister group to a clade that comprises (Bulloidea (Haminoeoidea, Cylichnoidea)). There is strong support for several previously suggested, but tenuously supported relationships such as the genus Odontoglaja nesting within the family Aglajidae, and a sister group relationship between Gastropteridae and Colpodaspididae, with Philinoglossidae as their sister group. We discuss these results and their implications in the context of current cephalaspidean taxonomy and evolution. Genomic-scale data give a backbone to this group of snails and slugs, and hold promise for a completely resolved Cephalaspidea., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Sea slugs are interesting models to study post-copulatory sexual selection in simultaneous hermaphrodites due to the enormous variation of their reproductive systems. However, the knowledge of the functional morphology of their reproductive system is limited to few species, and it is rarely discussed in the context of sexual selection theory. In this study, we investigated the functional morphology of the sperm-containing chambers (i.e., ampulla, seminal receptacle, and bursa copulatrix) of the reproductive system of Okenia polycerelloides (Ortea & Bouchet, 1983), based on light, confocal, and electron microscopy. Although the morphology of the ampulla is similar to other species, indicating that it is a site for autosperm storage, we found some sperm facing the ampullar epithelium, a feature commonly regarded as characteristic of the seminal receptacle of sea slugs. The seminal receptacle of O. polycerelloides showed secretory activity and contained sperm with distribution and orientation suggestive of stratification of allosperm from distinct mating events, a feature that would affect sperm competition. The bursa copulatrix had epithelial cells with secretory and absorptive characteristics, and contained degraded sperm and yolk granules within its lumen. Comparative analyses of the contents of each organ demonstrated that sperm digestion occurs in the bursa copulatrix and affects sperm heads first, changing their morphology from slender and curved to shorter and ellipsoid before complete lysis. Although digestion and absorption of surplus sperm are currently the main hypothesized functions for the bursa copulatrix, its role in cryptic female choice should not be ruled out. The close structural connection between the seminal receptacle and bursa copulatrix, as well as their muscular walls, would enable control over the fate of the sperm received in each mating event, that is, storage or digestion., (© 2020 Wiley Periodicals LLC.)

The radula is the basic feeding structure in gastropod molluscs and exhibits great morphological diversity that reflects the exceptional anatomical and ecological diversity occurring in these animals. This uniquely molluscan structure is formed in the blind end of the radular sac by specialized cells (membranoblasts and odontoblasts). Secretion type, and the number and shape of the odontoblasts that form each tooth characterize the mode of radula formation. These characteristics vary in different groups of gastropods. Elucidation of this diversity is key to identifying the main patterns of radula formation in Gastropoda. Of particular interest would be a phylogenetically closely related group that is characterized by high variability of the radula. One such group is the large monophyletic superfamily Conoidea, the radula of which is highly variable and may consist of the radular membrane with five teeth per row, or the radular membrane with only two or three teeth per row, or even just two harpoon-like teeth per row without a radular membrane. We studied the radulae of two species of Conoidea (Clavus maestratii Kilburn, Fedosov & Kantor, 2014 [Drilliidae] and, Lophiotoma acuta (Perry, 1811) [Turridae]) using light and electron microscopy. Based on these data and previous studies, we identify the general patterns of the radula formation for all Conoidea: the dorsolateral position of two groups of odontoblasts, uniform size, and shape of odontoblasts, folding of the radula in the radular sac regardless of the radula configuration. The morphology of the subradular epithelium is most likely adaptive to the radula type., (© 2020 Wiley Periodicals LLC.)

The most common European gastropod species, Arion vulgaris, is one of the most troublesome pests for private garden owners and commercial agriculturists. The sticky and hard to remove secretion produced by these animals allows them to overcome most artificial and natural barriers. However, this highly adherent biopolymer has recently shown great potential for novel wound-healing applications in medicine. Nevertheless, our knowledge of the underlying gland system is still limited and few studies on the ventral gland system are available. We studied the lateral and ventral pedal glands in Arion vulgaris to determine their secretory content histochemically and through lectin assays. Using these histological and histochemical methods we differentiate five gland types with different mucus composition in the lateral pedal region of the foot of Arion vulgaris. These contain sulphated and carboxylated mucosubstances (positive Alcian blue staining) but lack hexose-containing mucosubstances (negative PAS staining). In the ventral pedal region, four gland types can be differentiated producing sulphated and carboxylated mucosubstances. Within the ventral mucus, a high affinity for the lectins PNA and WGA is observed. While the lateral glands are histochemically negative for PAS, a positive staining with the lectin JAC is observed. Arion vulgaris shows clear morphological differences from other arionid species. This raises the question whether the variation in the chemistry of the secretory material and mucus composition is the result of different functions and/or is related to the animals' different environmental conditions. A comparison of some glands of Arion vulgaris with those of the helicid species Helix pomatia and Cepaea hortensis indicates morphological similarities., (© 2020 The Authors. Journal of Morphology published by Wiley Periodicals LLC.)

The pattern of shell shape variation in populations of the top shell, Phorcus sauciatus from Madeira Island (NE Atlantic) was analysed as a function of substrate type and wave exposure, using geometric morphometrics. We hypothesized that P. sauciatus shows morphological variations to inhabit contrasting environments. Highly significant differences in shell shape were found depending on both substrate type and coastal exposure. The most marked differences were found between exposed and sheltered environments. Rounded shells in exposed environments may be explained by physiological reasons, since larger muscles are needed to ensure attachment to substrate in areas subject to harsh conditions. On the other side, conically-shaped shells may accommodate a larger body but with a smaller foot, an adaptation to sheltered environments. Slight shape variations were also observed among substrates, mostly in the degree of differentiation of some whorls. Differences could be related to a particular use of habitat and/or to the degree of exposure to water current. These results suggest that P. sauciatus is locally adapted to varying coastal hydrodynamics and may be considered as a good model in studies on adaptations of fauna to certain climate change effects., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier GmbH. All rights reserved.)

Gastropod shells may present large spines and sharp shapes that vary according to environmental, taxonomic, and evolutionary factors. In these cases, classic morphometric methods used to study shell contour might not provide a clear representation of morphological shell based on angular decomposition of contour. The present study analyzed and compared for the first time the robustness of the contour analysis using wavelet transformed and Elliptic Fourier descriptors for gastropod shells including enlarged spines. For that, we analyzed two geographical and ecological separated populations of Bolinus brandaris from the NW Mediterranean Sea. Results showed that contour analysis of gastropod shells with enlarged spines can be analyzed using both methodologies, but the wavelet analysis provided a better local discrimination. From an ecological perspective, shells with spines of different sizes were observed in both localities suggesting a wide plasticity of the species., (Copyright © 2020 Elsevier GmbH. All rights reserved.)

Paedomorphosis is an important evolutionary force. It has previously been suggested that a soft-substrate sediment-dwelling (infaunal) environment facilitates paedomorphic evolution in marine invertebrates. However, until recently this proposal was never rigorously tested with robust phylogeny and broad taxon selection. Here, for the first time, we present a molecular phylogeny for a majority of the 21 families of one of the largest nudibranch subgroups (Aeolidacea) and show that the externally highly simplified vermiform nudibranch family, Pseudovermidae, with clearly defined paedomorphic traits and inhabiting a soft-substrata environment, is a sister group to the complex nudibranch family, Cumanotidae. We also report the rediscovery of one of the most enigmatic nudibranchs-Xenocratena suecica-on the Swedish and Norwegian coasts 70 years after it was first found. Xenocratena was described from the same location and environment in the Swedish Gullmar fjord as one of the most enigmatic vermiform organisms, Xenoturbella bocki, which represents either an original simple bilaterian body plan or secondary simplification of a more complex organisation. Our results show that Xenocratena suecica reveals an onset of parallel paedomorphic evolution so we have proposed the new family, Xenocratenidae fam. n., to accommodate the molecular and morphological disparities we discovered. The paedomorphic origin of another aeolidacean family, Embletoniidae, is also demonstrated for the first time. Thus, by presenting three independent lineages from non-closely related aeolidacean families, Xenocratenidae fam. n., Cumanotidae and Embletoniidae, we confirm with phylogenetic data that a soft-substrata burrowing-related environment strongly favours paedomorphic evolution. We suggest criteria to distinguish ancestral and derived characters in the context of modifications of ontogenetic cycles. Applying an evolutionary model of the soft substrate-driven multiple paedomorphic origin of several families of nudibranch molluscs we propose that it is plausible to extend this model to other marine invertebrates and suggest that the ancestral organisation of the enigmatic metazoan, Xenoturbella, might correspond to the larval part of a complex ancestral bilaterian ontogenetic cycle with sedentary/semi-sedentary adult stages and planula-like larval stages., Competing Interests: The authors have declared that no competing interests exist.

Macrocypraea mammoth is a new species from Trindade, a remote oceanic island located 1160 km off Espírito Santo, Brazil. This isolated species is described in a detailed morphological scenario that includes all Recent congeneric species. The detailed anatomy of two Recent species, M. zebra and M. cervinetta, were described in a previous paper. The remaining one, M. cervus, is included herein. Brief taxonomical comments on all these species is also included. The new species can be distinguished from other Western Atlantic species by its larger size, proportionally heavier and more solid shell, more rounded and wider outline, longer posterior tapered ending and slightly inflated base; anatomically it has some exclusivities, such as the mantle papillae mostly bearing 3-5 distal aligned projections, osphradium with a shorter branch, modifications in some odontophore muscles, penis with a clear glandular region, and a sac-like bursa copulatrix with a long duct. Based on the comparative analysis, the genus Macrocypraea can be defined by the wide distance between the osphradium and gill; a twofold buccal muscle (mc); a radular ventral tensor muscle (pair m11) surrounding radular sac; and a bursa copulatrix located at middle level of the pallial oviduct. Register ZooBank: urn:lsid:zoobank.org:pub:C8E6E515-508F-47DE-9753-4EA619C1DDFD., Competing Interests: The authors have declared that no competing interests exist.

Ocean acidification is mainly being monitored using data loggers which currently offer limited coverage of marine ecosystems. Here, we trial the use of gastropod shells to monitor acidification on rocky shores. Animals living in areas with highly variable pH (8.6-5.9) were compared with those from sites with more stable pH (8.6-7.9). Differences in site pH were reflected in size, shape and erosion patterns in Nerita chamaeleon and Planaxis sulcatus. Shells from acidified sites were shorter, more globular and more eroded, with both of these species proving to be good biomonitors. After an assessment of baseline weathering, shell erosion can be used to indicate the level of exposure of organisms to corrosive water, providing a tool for biomonitoring acidification in heterogeneous intertidal systems. A shell erosion ranking system was found to clearly discriminate between acidified and reference sites. Being spatially-extensive, this approach can identify coastal areas of greater or lesser acidification. Cost-effective and simple shell erosion ranking is amenable to citizen science projects and could serve as an early-warning-signal for natural or anthropogenic acidification of coastal waters., (Copyright © 2019. Published by Elsevier B.V.)

The systematics of Semisulcospiridae in China is revised here based on morphological characters and mitochondrial phylogenetics. Phylogenetic relationships within the Chinese semisulcospirids were assessed via DNA sequences from mitochondrial analysis (cytochrome c oxidase I and 16S rRNA). This research contains most morphospecies of semisulcospirids previously recorded in China. Based on these results, the family of Chinese Semisulcospiridae is represented by three genera: i.e., viviparous Semisulcospira Böttger, 1886, oviparous Hua Chen, 1943 and Koreoleptoxis Burch and Jung, 1988. These genera can be distinguished from each other by reproductive anatomy, reproductive mode, and radula features. Species of Hua are mainly distributed in southwest China and Guangxi, whereas Koreoleptoxis and Semisulcospira are mainly distributed in south and northeast China.

In vertebrates, the steroidogenesis enzyme 5α-reductase converts testosterone to the more potent androgen 5α-dihydrotestosterone. Homologues of 5α-reductase genes have been identified in molluscs. However, recent findings suggest that vertebrate-type steroid androgens are not utilised in molluscan reproductive development. Genomic searches have revealed that molluscs do not possess many of the steroidogenic enzymes required to make testosterone, nor a nuclear androgen receptor. Consequently, the role of 5α-reductase in molluscs presents a mystery. Here, developmental exposures of Biomphalaria glabrata to selective pharmaceutical 5α-reductase inhibitors elicited a strong, highly reproducible phenotypic response characterised by the development of elongated "banana-shaped" shell morphology. In comparison to untreated snails, the shells are open-coiled and the whorls are unattached. Dutasteride (5α-reductase inhibitor) is approximately 10-times more potent at provoking the banana-shaped shell phenotype than finasteride, paralleling the pharmaceuticals' efficacy in humans. Other enzyme inhibitors with different modes of action were tested to investigate the specificity of the phenotype. However, only the pharmaceutical 5α-reductase inhibitors provoked the response. Dutasteride elicited the same phenotype in a second gastropod, Physella acuta. In the absence of evidence for de novo androgen steroidogenesis in molluscs, these findings suggest that novel substrates for 5α-reductase exist in gastropods, lending support to the contention that molluscan endocrinology differs from the well-characterised vertebrate endocrine system.

The radular morphology of the patellid species Testudinalia testudinalis (O. F. Müller, 1776) from the White Sea was studied using light, electron, and confocal microscopy. The radula is of the docoglossan type with four teeth per row and consisting of six zones. We characterize teeth formation in T. testidinalis as follows: one tooth is formed by numerous and extremely narrow odontoblasts through apocrine secretion; this initially formed tooth consists of numerous vesicles; the synthetic apparatus of the odontoblasts is localized in the apical and central parts of the cells throughout the cytoplasm and is penetrated by microtubules which are involved in the transport of the synthesized products to the apical part of the odontoblast; the newly formed teeth consist of unpolymerized chitin. Mitotic activity is located in the lateral parts of the formation zone. The first four rows contain an irregular arrangement of teeth, but the radular teeth are regularly arranged after the fifth row. The irregularly arranged teeth early on could be a consequence of the asynchronous formation of teeth and the distance between the odontoblasts and the membranoblasts. The morphological data obtained significantly expands our knowledge of the morphological diversity of the radula formation in Gastropoda., (© 2019 Wiley Periodicals, Inc.)

Biological materials such as chiton tooth, squid beak, and byssal threads of bivalves have inspired the development of new technologies. To this end, we have characterized the acellular components in the buccal mass of the terrestrial slug Ariolimax californicus (banana slug). These components are the radula, the jaw, and the odontophore. In the radula, calcium-rich denticles are tightly interlocked one to the other on top of a nanofibrous chitin membrane. The jaw has a nanostructured morphology made of chitin to achieve compression resistance and is directly linked to the foregut cuticle, which has a protective nanofibrous structure. Finally, in the odontophore, we observed a structurally elastic microstructure that interfaces soft tissues with a highly stressed radula membrane. Based on those observations, we discuss the interaction between these components and highlight how the materials in these task-specific components have evolved. This structure-properties-function study of the A. californicus' buccal mass may aid in the design and fabrication of novel bioinspired materials., Competing Interests: The authors have declared that no competing interests exist.

Juga is a genus of freshwater gastropods distributed in Pacific and Interior drainages of the Pacific Northwest from central California to northern Washington. The current classification has relied heavily on features of the shell, which vary within and across drainages, and often intergrade without sharp distinctions between species. The only previous molecular analysis included limited population sampling, which did not allow robust assessment of intra- versus interspecific levels of genetic diversity, and concluded almost every sampled population to be a distinct OTU. We assembled a multilocus mitochondrial (COI, 16S) and nuclear gene (ITS1) dataset for ∼100 populations collected across the range of the genus. We generated primary species hypotheses using ABGD with best-fit model-corrected distances and further explored our data, both individual gene partitions and concatenated datasets, using a diversity of phylogenetic and species delimitation methods (Bayesian inference, maximum likelihood estimation, StarBEAST2, bGMYC, bPTP, BP&P). Our secondary species delimitation hypotheses, based primarily on the criterion of reciprocal monophyly, and informed by a combination of geography and morphology, support the interpretation that Juga comprises a mixture of geographically widespread species and narrow range endemics. As might be expected in taxa with low vagility and poor dispersal capacities, analysis of molecular variance (AMOVA) revealed highly structured populations with up to 80% of the observed genetic variance explained by variation between populations. Analyses with bGMYC, bPTP, and BP&P appeared sensitive to this genetic structure and returned highly dissected species hypotheses that are likely oversplit. The species diversity of Juga is concluded to be lower than presently recognized, and the systematics to require extensive revision. Features of the teleoconch considered significant in species-level and subgeneric classification were found to be variable within some species, sometimes at a single site. Of a number of potentially new species identified in non-peer reviewed reports and field guides, only one was supported as a distinct OTU., (Published by Elsevier Inc.)

The genera Angustipes Colosi, 1922 and Latipes Colosi, 1922 were originally proposed as "groups" within the genus Vaginulus Ferrussac, 1822, and since their establishment they have been variously considered valid or invalid until they gained the ultimate status of genus. The descriptions of both genera are general and broadly inclusive, and this fact has complicated taxonomic recognition. Additionally, incomplete descriptions and difficult identification of characteristics in the name-bearing type specimens demonstrate the need to revisit the species and revise the two genera. Herein, we broaden the description of Latipes erinaceus Colosi, 1922 with respect to the circulatory system, the radula, the jaw, the position of entry of the ligation duct in the bursa copulatrix in relation to the canal of the bursa, the origin of the muscle of the penial gland, along with the morphometric characteristics of the phallus, the penial gland, the pedal gland, and the bursa copulatrix. We also propose new differential diagnoses for the genera Angustipes and Latipes, limited to the essential characteristics that enable taxonomic recognition. Hence, we propose the assignment of the species L. erinaceus, Latipes rosilus (Thiele, 1927), Latipes ribeirensis (Thiele, 1927), and Latipes absumptus (Colosi, 1921) to the genus Angustipes , based on the presence of morphological characteristics attributable to this genus, such as the phallus being short and conical; the bursa copulatrix being sessile or short, and lacking a head; the ligation duct inserted near the canal of the bursa; as well as on the similarity in phallus morphology with Angustipes difficilis Colosi, 1922, the type species of this genus., (© 2019 Zoological Society of Japan.)

The precise number of Okenia taxa inhabiting the Mediterranean Sea, as well as their general taxonomy, varies according to different specialists. So far, eight valid species have been reported from the area: Okenia aspersa (Alder & Hancock, 1845), Okenia cupella (Vogel & Schultz, 1970), Okenia elegans (Leuckart, 1828), Okenia hispanica Valdés & Ortea, 1995, Okenia impexa Er. Marcus, 1957, Okenia leachii (Alder & Hancock, 1854), Okenia mediterranea (Ihering, 1886), and Okenia zoobotryon (Smallwood, 1910). Of these, only three (O. elegans, O. hispanica, and O. mediterranea) have their type localities in the Mediterranean Sea, whereas the others were described from different biogeographic areas and later included in the Mediterranean biota. We carried out a review on Mediterranean Okenia species through an integrative approach, based on a wide literature search and a morphological and molecular analysis of available type material and samples collected recently. The present study confirmed the presence of O. aspersa, O. elegans, O. hispanica, and O. mediterranea in the Mediterranean Sea, although leaving remaining questions about some of those taxa. The distribution of O. cupella, O. impexa, and O. zoobotryon is limited to the western Atlantic, and of O. leachii to the eastern Atlantic. All specimens previously identified as O. cupella, O. impexa, and O. zoobotryon by different authors in the Mediterranean Sea were repeatedly misidentified. Thus, we describe Okenia problematica sp. nov. and Okenia longiductis sp. nov., from the "Mediterranean" Okenia cupella/impexa and O. zoobotryon. We also consider here Okenia pusilla Sordi, 1974 a nomen dubium and include a redescription of the holotype of O. cupella. A molecular phylogeny, including all the sequenced Okenia species, was performed in order to evaluate the evolutionary relationships of the newly described species with the other congeneric taxa., Competing Interests: The authors have declared that no competing interest exist.

Recent phylogenetic revisions of euthyneuran gastropods ("opisthobranchs" and "pulmonates") suggest that clades with a planktotrophic larva, the ancestral life history for euthyneurans, are more widely distributed along the trunk of the euthyneuran tree than previously realized. There is some indication that the planktotrophic larva of euthyneurans has distinctive features, but information to date has come mainly from traditional "opisthobranch" groups. Much less is known about planktotrophic "pulmonate" larvae. If planktotrophic larvae of "pulmonates" share unique traits with those of "opisthobranchs," then a distinctive euthyneuran larval-type has been the developmental starting template for a spectacular amount of evolved morphological and ecological disparity among adult euthyneurans. We studied development of a siphonariid by preparing sections of larval and postmetamorphic stages for histological and ultrastructural analysis, together with 3D reconstructions and data from immunolabeling of the larval apical sensory organ. We also sought a developmental explanation for the unusual arrangement of shell-attached, dorso-ventral muscles relative to the mantle cavity of adult siphonariids. Adult siphonariids ("false limpets") have a patelliform shell but their C-shaped shell muscle partially embraces a central mantle cavity, which is different from the arrangement of these components in patellogastropods ("true limpets"). It is not obvious how shell muscles extending into the foot become placed anterior to the mantle cavity during siphonariid development from a veliger larva. We found that planktotrophic larvae of Siphonaria denticulata are extremely similar to previously described, planktotrophic "opisthobranch" larvae. To emphasize this point, we update a list of distinctive characteristics of planktotrophic euthyneuran larvae, which can anchor future studies on the impressive evolvability of this larval-type. We also describe how premetamorphic and postmetamorphic morphogenesis of larval mantle fold tissue creates the unusual arrangement of shell-muscles and mantle cavity in siphonariids. This result adds to the known postmetamorphic evolutionary innovations involving mantle fold tissue among euthyneurans., (© 2019 Wiley Periodicals, Inc.)