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Gastropods have survived several mass extinctions during their evolutionary history resulting in extraordinary diversity in morphology, ecology, and developmental modes, which complicate the reconstruction of a robust phylogeny. Currently, gastropods are divided into six subclasses: Caenogastropoda, Heterobranchia, Neomphaliones, Neritimorpha, Patellogastropoda, and Vetigastropoda. Phylogenetic relationships among these taxa historically lack consensus, despite numerous efforts using morphological and molecular information. We generated sequence data for transcriptomes derived from 12 taxa belonging to clades with little or no prior representation in previous studies in order to infer the deeper cladogenetic events within Gastropoda and, for the first time, infer the position of the deep-sea Neomphaliones using a phylogenomic approach. We explored the impact of missing data, homoplasy, and compositional heterogeneity on the inferred phylogenetic hypotheses. We recovered a highly supported backbone for gastropod relationships that is congruent with morphological and mitogenomic evidence, in which Patellogastropoda, true limpets, are the sister lineage to all other gastropods (Orthogastropoda) which are divided into two main clades 1) Vetigastropoda s.l. (including Pleurotomariida + Neomphaliones) and 2) Neritimorpha + (Caenogastropoda + Heterobranchia). As such, our results support the recognition of five subclasses (or infraclasses) in Gastropoda: Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda, and Heterobranchia. [Compositional heterogeneity; fast-evolving; long-branch attraction; missing data; Mollusca; phylogenetics; systematic error.]

Takano, Tsuyoshi, Tsuzuki, Shouji, Kano, Yasunori (2022): Description of a second species of the eulimid genus Concavibalcis (Gastropoda: Vanikoroidea). Zootaxa 5093 (3): 397-400, DOI: https://doi.org/10.11646/zootaxa.5093.3.8

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.

The family Cocculinidae (Gastropoda: Cocculinida) consists of small, usually colourless benthic limpets living primarily at depths below 100 m, and on decaying plant or animal remains. These habitats are difficult to sample and the knowledge about Cocculinidae species diversity, biogeography, ecology and evolution is therefore poor. To explore the species diversity of the Cocculinidae, we examined 499 specimens collected from 196 sites, mainly explored during expeditions of the ‘Tropical Deep-Sea Benthos’ programme in the Indo-West Pacific (IWP). To propose a species hypotheses, we used an integrated approach to taxonomy in which we combined DNA-based methods, with morphological, geographical and ecological considerations. To classify the species hypotheses into genera, we used a combination of one mitochondrial and two nuclear gene fragments to reconstruct a phylogenetic tree. We then used six morphological characters to diagnose the identified genera. Our results revealed an exceptionally high diversity of IWP Cocculinidae, with 51 species hypotheses that were mostly not assigned to available species names. We also discovered a previously unknown type of copulatory structure in the group. At a higher taxonomic level, we identified ten main clades in the family. Although six of them matched existing genera, four others should be regarded as new genera awaiting formal description.

The phylogenetic position of Haloceratidae, a little-known family of the subclass Caenogastropoda, is contested due to its extreme rarity in bathyal waters worldwide (c. 800–3,500 m deep). Haloceratids share several morphological and ecological traits with members of Vanikoroidea, Tonnoidea, Capuloidea and Velutinoidea, and were provisionally included in Vanikoroidea based on the absence of certain apomorphic features of the latter three taxa. Here, we first investigate the phylogenetic position of the family based on molecular data from both of the recognized genera, Haloceras and Zygoceras. Reconstruction based on three nuclear and three mitochondrial gene sequences suggests that the Haloceratidae constitute a sister clade to the Capulidae and that the two families collectively form the superfamily Capuloidea. This superfamily is united in a large, robust clade with Calyptraeoidea, Velutinoidea, Tonnoidea and Neogastropoda. The superfamily Cypraeoidea, as previously conceived, was found to be polyphyletic; we propose new concepts of Cypraeoidea (including Cypraeidae and Ovulidae) and Velutinoidea (including Velutinidae, Eratoidae and Triviidae). This topology also confirms the polyphyly of taxa with the ‘echinospira’ type of larvae (Echinospirida). The morphological resemblance of these polyphyletic taxa highlights parallel acquisition of traits in response to the same selective pressures.

The mitochondrial genome of the neritid snail Nerita (Heminerita) japonica (Mollusca: Neritimorpha) from Kumamoto, Japan was determined by whole-genome sequencing. This mitogenome is comprised of 13 protein-coding genes, 2 ribosomal RNA (12S and 16S) genes, and 22 transfer RNA genes, with the same gene order as in the other species of the family Neritidae. A likelihood-based phylogenetic reconstruction recovered the subgenus Heminerita (including N. japonica as its type and N. yoldii from China) as monophyletic and sister to a clade with four species of the subgenera Nerita and Theliostyla.

The assignment of species to the vetigastropod genus Solariella Wood, 1842, and therefore the family Solariellidae Powell, 1951, is complicated by the fact that the type species (Solariella maculata Wood, 1842) is a fossil described from the Upper Pliocene. Assignment of species to genera has proved difficult in the past, and the type genus has sometimes acted as a ‘wastebasket’ for species that cannot easily be referred to another genus. In the light of a new systematic framework provided by two recent publications presenting the first molecular phylogenetic data for the group, we reassess the shell characters that are most useful for delimiting genera. Shell characters were previously thought to be of limited taxonomic value above the species level, but this is far from the case. Although overall shell shape is not a reliable character, our work shows that shell characters, along with radular and anatomical characters, are useful for assigning species to genera. Sculpture of the early teleoconch (the region immediately following the protoconch) and the columella are particularly useful characters that have not been used regularly in the past to distinguish genera. However, even with the combination of all morphological characters used in this study (shell, radular and eye), a few species are still difficult to assign to genera and in such cases molecular systematic data are essential. In the present study, we discuss 13 genera—12 of which were recovered as well-supported clades in recent molecular systematic studies—and provide morphological characters to distinguish them. We describe several new taxa: Chonospeira n. gen. (referred to as ‘clade B’ in previous molecular systematic studies), Phragmomphalina n. gen. (Bathymophila in part in molecular systematic studies) and Phragmomphalina vilvensi n. sp. (type species of Phragmomphalina n. gen.). We synonymize Hazuregyra Shikama, 1962 with Minolia A. Adams, 1860, Minolia subangulata Kuroda & Habe, 1952 with Minolia punctata A. Adams, 1860 and M. gemmulata Kuroda & Habe, 1971 with M. shimajiriensis (MacNeil, 1960). We also present the following new combinations: Bathymophila bairdii (Dall, 1889), B. dawsoni (Marshall, 1979), B. regalis (Marshall, 1999), B. wanganellica (Marshall, 1999), B. ziczac (Kuroda & Habe in Kuroda, Habe & Oyama, 1971), Chonospeira nuda (Dall, 1896), C. iridescens (Habe, 1961), C. ostreion (Vilvens, 2009), C. strobilos (Vilvens, 2009), Elaphriella corona (Lee & Wu, 2001), E. diplax (Marshall, 1999), E. meridiana (Marshall, 1999), E. olivaceostrigata (Schepman, 1908), E. opalina (Shikama & Hayashi, 1977), Ilanga norfolkensis (Marshall, 1999), I. ptykte (Vilvens, 2009), I. zaccaloides (Vilvens, 2009), Minolia shimajiriensis (MacNeil, 1960), M. watanabei (Shikama, 1962), Phragmomphalina alabida (Marshall, 1979), P. diadema (Marshall, 1999), P. tenuiseptum (Marshall, 1999), Spectamen euteium (Vilvens, 2009), S. basilicum (Marshall, 1999), S. exiguum (Marshall, 1999) and S. flavidum (Marshall, 1999).

We present the most comprehensive phylogeny of a globally distributed deep-sea group of gastropods published to date including over 80% of the recognized diversity of the family Scaphandridae. The definition and taxonomic composition of the Scaphandridae has been hampered by the lack of a sound phylogenetic framework and definition of synapomorphic traits. We used a combination of molecular phylogenetics (Bayesian Inference and Maximum Likelihood) based on five gene markers (cytochrome c oxidase subunit I, 12S rRNA, 16S rRNA, 18S rRNA, and 28S rRNA) and morpho-anatomical characters to redefine the Scaphandridae and its genera. A new classification is proposed with the three genera Nipponoscaphander, Sabatia, and Scaphander. Main differences between genera lie on the shells (shape, parietal callus, spire) and male reproductive system (prostate). The species Hamineobulla kawamurai is reassigned to the closely related family Eoscaphandridae, currently defined mostly based on pleisiomorphic traits. Biogeographically the genus Nipponoscaphander is restricted to the Indo-West Pacific; Sabatia is mostly circumscribed to the Indo-West Pacific, but has one lineage present in the north Atlantic Ocean. Polyphyly across ocean realms prevails in the specious and globally distributed genus Scaphander with multiple speciation events between Indo-Pacific and Atlantic lineages but also with several episodes of cladogenesis within realms. Two rare cases of species with a broad distribution spanning the Indo-West Pacific and Atlantic realms are confirmed (S. meridionalis and S. nobilis).

We present a complete mitochondrial genomic sequence for the tanaidacean Arctotanais alascensis (Richardson, 1899); this is the first complete mitogenome reported from the order Tanaidacea. The mitogenome is 13,988 bp long and contains 13 protein coding and two ribosomal RNA genes (as is typical for animal mitogenomes), and 21 of 22 transfer RNAs; we did not detect an isoleucine transfer RNA (trnI) gene. The gene order differed markedly from the hypothetical ground pattern for Pancrustacea; only four clusters (trnM + nad2; trnC + trnY + cox1 + trnL2 + cox2; trnD + atp8 + atp6 + cox3; trnH + nad4 + nad4l) ancestrally present were retained. In a malacostracan phylogenetic tree reconstructed from mitogenome data, basal relationships were marginally supported or incongruent with the traditional morphology-based classification and the latest phylogenetic reconstructions from large transcriptomic datasets. Relationships involving more recent divergences were better supported in our tree, suggesting that complete mitogenome sequences are more suitable for phylogenetic analyses within malacostracan orders, presumably including Tanaidacea.

The complete mitochondrial genome of the stream neritid Clithon retropictus was determined by next-generation sequencing. The mitochondrial genome is 15,814 bp in length, comprising two ribosomal RNA genes, 13 protein-coding genes (PCGs) and 22 transfer RNA genes (tRNAs). Of these 37 genes identified, 7 PCGs and 8 tRNAs are encoded on the heavy strand and the other genes on the light strand. This gene order is consistent with the previously published mitochondrial genomes of the other neritid species. This is the first report of a complete mitochondrial genome sequence for the genus and the fourth for the gastropod subclass Neritimorpha.

The superfamily Buccinoidea is distributed across the oceans of the world from the Arctic Ocean to the Antarctic and from intertidal to abyssal depths. It encompasses 3351 recent species in 337 genera. The latest taxonomic account recognized eight full families. For the first time, the monophyly of the superfamily and the relationships among the families are tested with molecular data supplemented by anatomical and radula data. Five genetic markers were used: fragments of mitochondrial COI, 16S rRNA, 12S rRNA and nuclear Histone 3 (H3) and 28S rRNA genes (for 225 species of 117 genera). Our analysis recovered Buccinoidea monophyletic in Bayesian analyses. The relationships between the formerly recognized families and subfamilies are drastically revised and a new classification of the superfamily is here proposed, now including 20 taxa of family rank and 23 subfamilies. Five new families (Chauvetiidae, Dolicholatiridae, Eosiphonidae, Prodotiidae and Retimohniidae) and one subfamily of Nassariidae (Tomliniinae) are described. Austrosiphonidae and Tudiclidae are resurrected from synonymy and employed in a new taxonomical extension. All but 40 recent genera are reclassified. Our results demonstrate that anatomy is rather uniform within the superfamily. With exceptions, the rather uniform radular morphology alone does not allow the allocation of genera to a particular family without additional molecular data.

We present a complete mitochondrial genomic sequence for the tanaidacean

The molluscan class Gastropoda includes over 5,000 parasitic species whose evolutionary origins remain poorly understood. Marine snails of the genus Caledoniella (Caledoniellidae) are obligate parasites that live on the abdominal surface of the gonodactylid mantis shrimps. They have highly modified morphological characteristics specialized to the ectoparasitic lifestyle that make it difficult to infer their close relatives, thereby posing a question about their current systematic position in the superfamily Vanikoroidea. In the present study, we performed molecular phylogenetic analyses using three nuclear and three mitochondrial gene sequences to unveil the phylogenetic position of these enigmatic snails. The resulting trees recovered Caledoniella in the superfamily Truncatelloidea and within a subclade of commensal species that live on the burrow wall of marine benthic invertebrates. More specifically, Caledoniella formed the sister clade to a commensal snail species living in mantis-shrimp burrows and they collectively were sister to Sigaretornus planus (formerly in the family Tornidae or Vitrinellidae), a commensal living in echiuran burrows. This topology suggests that the species of Caledoniella achieved their ectoparasitic mode of life through the following evolutionary pathway: (1) invasion into the burrows of benthic invertebrates, (2) specialization to mantis shrimps, and (3) colonization of the host body surface from the host burrow wall with the evolution of the parasitic nature. The final step is likely to have been accompanied by the acquisition of a sucker on the metapodium, the loss of the radula and operculum, and the formation of monogamous pair bonds. The present molecular phylogeny also suggested parallel evolution of planispiral shells in a subclade of Truncatelloidea and enabled us to newly redefine the families Caledoniellidae, Elachisinidae, Teinostomatidae, Tornidae and Vitrinellidae.

The Southwest Pacific represents an independent biogeographic province for deep-sea hydrothermal vent fauna. Different degrees of genetic connectivity among vent fields in Manus, North Fiji and Lau Basins have been reported for various molluscan and crustacean species, presumably reflecting their different levels of dispersal ability as swimming larvae. The present study investigates the population connectivity of the hydrothermal vent limpet Shinkailepas tollmanni (family Phenacolepadidae) in the Southwest Pacific. Our analyses using mitochondrial COI-gene sequences and shell morphometric traits suggest a panmictic population structure throughout its geographic and bathymetric ranges, spanning 4,000 km from the westernmost Manus Basin (151ºE; 1,300 m deep) to the easternmost Lau Basin (176ºE; 2,720 m). The measurements of its embryonic and larval shells demonstrate that the species hatches as a planktotrophic veliger larva with an embryonic shell diameter of 170-180 μm and settles at the vent environment with the larval shell diameter of 750-770 μm. This substantial growth as a feeding larva, ca. 80 times in volume, is comparable or even greater than those of confamilial species in the hydrothermal-vent and methane-seep environments in the Northwest Pacific and Atlantic Oceans. Large pigmented eyes in newly settled juveniles are another common feature in this and other phenacolepadids inhabiting the chemosynthetic environments. These results put together suggest that the larvae of S. tollmanni migrate vertically from deep-sea vents to surface waters to take advantages of richer food supplies and faster currents and stay pelagic for an extended period of time (> 1 year), as previously indicated for the confamilial species.

The joint Russian–German expedition SokhoBio in 2015, on the research vessel Akademik M.A. Lavrentyev, provided the first opportunity to investigate the richness and composition of the abyssal gastropod fauna in the Kuril Basin of the Sea of Okhotsk, from which only a single species has been recorded in the literature. During the expedition, sampling of benthic animals was conducted at eight stations in the Sea of Okhotsk and at three stations in the Pacific (landward slope of the Kuril–Kamchatka Trench) using an Agassiz trawl, an epibentic sledge, and a giant box corer. A total of 417 specimens of ‘prosobranch’ gastropods were taken alive and were classified into 15 families and 70 species of Vetigastropoda and Caenogastropoda. Both abundance and richness were lower than expected in the Kuril Basin compared to the Pacific: 97 specimens belonging to 27 species (11 families) were collected at seven stations in the Kuril Basin, while 286 specimens in 43 species were found from two abyssal stations on the Pacific side of the Kuril Islands. Only six species occurred at abyssal depths on both sides. Familial composition also differed: large-sized buccinids were common only on the Pacific side. The very low levels of dissolved oxygen might explain the low abundance and richness, as well as the scarcity of large species, of Gastropoda in the Kuril Basin.

The red-blooded limpet ‘Shinkailepas’briandi(Neritimorpha: Phenacolepadidae) is one of the commonest gastropod species at deep-sea hydrothermal vents on the Mid-Atlantic Ridge (MAR). We investigated its population connectivity along MAR as the first such study for gastropods and explored the importance of larval migration for the distribution of vent-endemic animals. Our analyses, based on 1.3-kbp DNA sequences from the mitochondrial COI gene, showed a panmictic population throughout its geographic and bathymetric ranges that span from the northernmost and shallowest Menez Gwen vent field (38°N; 814–831 m depth) to the southernmost and deepest Ashadze field (13°N; 4090 m). Early development of this species is presumed to have a long pelagic duration as a planktotrophic larva; the hatchling with a shell diameter of 170–180 μm attains a constant settlement size of 706 ± 8 μm (mean ± SD). Retention of eye pigmentation in newly settled juveniles, along with the genetic panmixia, suggests that the hatched larva of ‘S.’briandimigrates vertically to the surface water, presumably to take advantage of richer food supplies and stronger currents for dispersal, as has been shown for confamilial species at hydrothermal vents and cold methane seeps.

An eulimid gastropod, Megadenus atrae n. sp., endoparasitic in the cloacal chamber of the black sea cucumber Holothuria atra Jaeger is described from Okinawa, Japan, as the fifth species of the genus. Conspecific specimens have also been found from southeast India, northeast Australia and New Caledonia. The generic assignment is justified by the presence of (i) a thick, long proboscis that bears a large fold (pseudopallium) near the base and a collar-like structure at the middle, (ii) a thin, globose shell that is covered by the pseudopallium, and (iii) sexual dimorphism with the female generally larger than the male. The new species is distinguishable from the four previously described congeners by its cauldron-shaped pseudopallium, moderately-developed collar of the proboscis and rounded basal lip of the shell. The comparisons of the size and sex of solitary and paired individuals support a previous hypothesis that the species of Megadenus Rosén, 1910 are protandrous with environmental sex determination. The present species occurs mostly as monogamous pairs despite its very low population density, implying that the presence of a conspecific individual acts as a cue for larval settlement. Both mechanisms would increase individual reproductive success in such permanent parasites with low prevalence and abundance as the species of Megadenus.

The practice of species delimitation using molecular data commonly leads to the revealing of species complexes and an increase in the number of delimited species. In a few instances, however, DNA-based taxonomy has led to lumping together of previously described species. Here, we delimit species in the genus Cryptogemma (Gastropoda: Conoidea: Turridae), a group of deep-sea snails with a wide geographical distribution, primarily by using the mitochondrial COI gene. Three approaches of species delimitation (ABGD, mPTP and GMYC) were applied to define species partitions. All approaches resulted in eight species. According to previous taxonomic studies and shell morphology, 23 available names potentially apply to the eight Cryptogemma species that were recognized herein. Shell morphometrics, radular characters and geographical and bathymetric distributions were used to link type specimens to these delimited species. In all, 23 of these available names are here attributed to seven species, resulting in 16 synonymizations, and one species is described as new: Cryptogemma powelli sp. nov. We discuss the possible reasons underlying the apparent overdescription of species within Cryptogemma, which is shown here to constitute a rare case of DNA-based species lumping in the hyper-diversified superfamily Conoidea.

A new parasitic species of eulimid gastropod, Haliella seisuimaruaesp. nov., is described from bathyal (728–978 m) waters off the Pacific coasts of Japan. It shows the closest resemblance to the type species H. stenostoma from the North Atlantic and Barents Sea in having a tall shell with an almost straight outer lip, but differs in having a junction of the parietal wall and columellar lip at 38% of the aperture height from the suture (33% in H. stenostoma), a slightly wider aperture and a more curved and extended columellar lip. The holotype of H. seisuimaruaesp. nov. was found attached to an irregular sea urchin, Brissopsis sp. cf. luzonica (Spatangoida: Brissidae). This represents the first direct observation of parasitic ecology and echinoderm host for the genus Haliella. A new replacement name, Eulima tsushimensisnom. nov., is proposed here for Eulima stenostoma A. Adams, 1861, which is preoccupied by Eulima stenostoma Jeffreys, 1858 (type of Haliella).

Members of the gastropod superfamily Stromboidea (Littorinimorpha) are characterised by their elaborate shell morphologies, distinctive mode of locomotion, and often large and colourful eyes. This iconic group comprises over 130 species, including many large and charismatic species. The family Strombidae is of particular interest, largely due to its commercial importance and wide distribution in tropical and subtropical waters. Although a few strombid mitochondrial genomes have been sequenced, data for the other four Recent families in Stromboidea are lacking. In this study we report seven new stromboid mitogenomes obtained from transcriptomic and genomic data, with taxonomic representation from each Recent stromboid family, including the first mitogenomes for Aporrhaidae, Rostellariidae, Seraphsidae and Struthiolariidae. We also report a new mitogenome for the family Xenophoridae. We use these data, along with published sequences, to investigate the relationships among these and other caenogastropod groups. All analyses undertaken in this study support monophyly of Stromboidea as redefined here to include Xenophoridae, a finding consistent with morphological and behavioural data. Consistent with previous morphological and molecular analyses, including those based on mitogenomes, monophyly of Hypsogastropoda is confirmed but monophyly of Littorinimorpha is again rejected.

The gastropod superfamily Lepetelloidea represents an extremely diverse lineage in terms of their utilization of different deep-sea organic substrates that include sunken wood, leaves, whale and fish bones, egg cases of sharks and rays, annelid tubes and detrital cephalopod beaks among others. They also inhabit cold seeps and hydrothermal vents, thus presenting an interesting case for the evaluation of such organic substrates as ‘stepping stones’ into these chemosynthetically nourished environments. Here we show the first molecular phylogeny of the Pseudococculinidae, a primarily wood-dwelling family and the most speciose in Lepetelloidea. Special emphasis is placed on the genus Caymanabyssia, for which the only subfamily Caymanabyssiinae has been established, and a new species Caymanabyssia solis is described herein and compared with previously known taxa in order to reconsider the morphological characteristics of lepetelloids on wood. Bayesian and likelihood trees reconstructed using four-gene sequences reveal that Pseudococculinidae sensu auctt. is a polyphyletic taxon that is grouped by shared plesiomorphic conditions of characters including the radula, a digestive organ, the morphology of which is often governed strongly by diet and feeding ecology. The newly reinterpreted families Pseudococculinidae and Caymanabyssiidae represent reciprocal sister clades as a basal radiation in Lepetelloidea. Sunken wood might thus have served as an ancestral habitat from which species on other substrates and vent and seep taxa were derived.

Gastropods of the family Ellobiidae are an interesting group in which to study transitions from intertidal to terrestrial realms. However, the phylogenetic relationships within this family still lack resolution. We present a phylogenetic hypothesis of the Ellobiidae based on Bayesian and maximum likelihood phylograms. We used nuclear (18S, 28S, H3) and mitochondrial (16S, 12S, COI) data, increasing the numbers of markers and data, and making this the most comprehensive phylogenetic study of the family to date. Our results support phylogenetic hypotheses derived from morphological data, and provide a supported framework to evaluate the internal relationships within Ellobiidae. The resulting phylogenetic trees support the previous hypothesis that the Ellobiidae are monophyletic only if the Trimusculinae (Otina, Smeagol and Trimusculus) are considered part of this family. In addition, we found that the Carychiinae, Ellobiinae and Pythiinae are reciprocally monophyletic and closely related, with the Carychiinae as sister group to Ellobiinae. Relationships within Melampodinae and Pedipedinae and their phylogenetic positions remain unresolved. Land invasion by the Ellobiidae occurred independently in Carychiinae and Pythia during different geological times (Mesozoic and Cenozoic, respectively). Diversification in the family does not appear to be related to past climate and biotic changes, neither the Cretaceous-Paleogene boundary nor the lowering of the sea level in the Oligocene.

Fissurellidae are marine gastropods with a worldwide distribution and a rich fossil record. We integrate molecular, geographical and fossil data to reconstruct the fissurellid phylogeny, estimate divergence times and investigate historical routes of oceanic dispersal. With five molecular markers for 143 terminals representing 27 genera, we resolve deep nodes and find that many genera (e.g., Emarginula, Diodora, Fissurella) are not monophyletic and need systematic revision. Several genera classified as Emarginulinae are recovered in Zeidorinae. Future work should prioritize emarginuline genera to improve understanding of ancestral traits and the early evolution of fissurellids. Tree calibration with the fossilized birth-death model indicates that crown fissurellids originated around 175 Ma, and generally resulted in younger ages for the earliest nodes than the node dating approach. Model-based biogeographic reconstruction, supported by fossils, infers an Indo-West Pacific origin, with a westward colonization of new oceans via the Tethys Seaway upon the breakup of Pangea. Western Atlantic clades then served as source for dispersal towards other parts of the globe. As the sister group to all other fissurellids, Rimula is ranked in its own subfamily, Rimulinae stat. nov. New synonyms: Hemitominae syn. nov. of Zeidorinae stat. nov.; Cranopsissyn. nov. of Puncturella; Variegemarginulasyn. nov. of Montfortula.

Invasion of the land has been a considerable challenge for aquatic organismal lineages, primarily because of desiccation and lack of physical support in air. Gastropod molluscs are among the most successful animals in this habitat shift because of their hard exoskeleton, whereas land slugs, regarded as descendants of land snails, gradually lost their shells in sheltered, moist environments. We present solid evidence of terrestrial invasion by a lineage of sea slugs; this invasion is represented by a newly discovered species, Aiteng marefugitus (Panpulmonata: Acochlidia), from a humid tropical rainforest on a small island in the Republic of Palau, western Pacific. The slug lineage seems to have invaded the forest habitat directly from the upper littoral zone in the Cenozoic.

We examined morphological and molecular characteristics of individuals of Macroramphosus in Japanese waters (the East China Sea and the northwestern Pacific). Two morphotypes (M. scolopax-type and M. gracilis-type) that were differentiated based on 10 quantitative morphological characters were not supported by molecular analyses using nuclear and mitochondrial DNA markers, while a genetic deviation was observed between populations of Macroramphosus from the northwestern Pacific and the northeastern Atlantic. Macroramphosus scolopax-type and M. gracilis-type individuals are thought to be intraspecific morphotypes adapted to plankton and benthos feeding, respectively.

The gastropod family Eulimidae has attracted considerable attention as one of the most diverse groups of parasitic molluscs in terms of number of species and ranges of body plans and parasitic strategies. However, the phylogenetic position of the family has not been established within the Hypsogastropoda and this has hampered the inference of ancestral states in the evolution of the morphology and parasitic strategies. Here we present Bayesian and maximum likelihood phylograms of Hypsogastropoda based on nuclear and mitochondrial loci (18S and 28S rRNA, Histone H3, COI and 16S rRNA) and a better taxonomic sampling than in previous molecular analyses, to determine the position of Eulimidae. The resulting trees suggest Vanikoridae as the sister group of Eulimidae; the two families are collectively placed in the newly redefined superfamily Vanikoroidea, with Truncatelloidea and (potentially paraphyletic) Rissooidea as closest relatives. Vanikorids are protandrous hermaphrodites as are many eulimids and are essentially carnivorous, differing from the mostly gonochoristic and herbivorous/detritivorous Truncatelloidea and Rissooidea. The mode of feeding may have a phylogenetic signal also within Eulimidae, where radula-less species constitute a robust clade. Other new findings include a close affinity of the submarine-cave Pickworthiidae to Cerithioidea and a terminal position of Nystiellidae within the paraphyletic Epitoniidae.

The joint German–Russian expedition KuramBio II in 2016 provided a significant opportunity to reinvestigate the species composition and distribution of the abyssal and hadal gastropod fauna in the Kuril–Kamchatka Trench, which was sampled previously only by the Russian research vessel (R/V) Vityaz in the 1940–1960s. During the cruise of the German R/V Sonne, benthic animals were collected using an Agassiz trawl, an epibentic sledge, a multiple corer and a giant box corer. A total catch of 592 live specimens of non-heterobranch gastropods were classified into 86 species and 22 families of the subclasses Neomphaliones, Vetigastropoda, and Caenogastropoda. The abundance, richness and phylogenetic diversity were lower in the hadal zone than in the abyssal zone. Seven hadal stations (6,442–9,584 m) yielded a total of 101 specimens belonging to 22 species in 11 families, whereas catches from four abyssal stations on the landward and seaward slopes (5,102–6,221 m) included 491 specimens and 70 species in 21 families. The abundance, richness and diversity for the hadal zone are, however, particularly high in comparison with other oceanic trenches, due, presumably, to high primary production in the surface layer of the subarctic Northwest Pacific. The uniqueness of species composition increased with depth; sixteen out of the 22 species from the hadal stations (72.7%) were found exclusively in this depth zone. Two unnamed species of Neomphalidae and Sahlingia from 9,577 to 9,584 m represent the world’s deepest records for Neomphaliones and Vetigastropoda and suggest the as yet unidentified presence of the world-deepest cold-seep habitats in the Kuril–Kamchatka Trench.

Body size during larval development is one of the most important attributes of aquatic animals. The optimal size for changing form or habitat may vary according to ecological traits of species, while phylogenetic constraints also play a significant role. The major goal of this study is to reveal the patterns in the settlement size of planktotrophic larvae in an archaic gastropod superorder Neritimorpha. We take advantage of the fact that size at various ontogenetic stages of neritimorphs can be rigorously estimated by measuring features of the adult opercula. This unique feature of neritimorphs has allowed us to generate the largest data set so far on larval settlement sizes within a group of marine invertebrates that recruit into very different post-metamorphic habitats. Eighty-eight species that represent most extant genera from rocky shores, seagrass beds, mangroves, estuaries, streams, submarine caves, deep-sea vents or seeps showed negligible intraspecific variation and considerable interspecific differences in settlement size, particularly between genera or families. Settlement size is determined primarily by phylogenetic constraints, while parallel evolution toward smaller sizes was shown to occur exclusively in four independent clades (two living and two extinct) of amphidromous snails with a marine larval period followed by a limnic adult phase. The smaller settlement size may possibly reduce the risk of being wafted away from the estuaries of their natal streams through less time achieving metamorphic competence, while ability to make occasional long-distance trips is retained by the presence of a sufficiently long delay period. This delay period also seems to obscure the possible correlation between settlement size and geographic distribution range of neritimorph species, both fully marine and amphidromous.

Yasunori Kano1, Hiroaki Fukumori1,2, Bastian Brenzinger3 and Anders Waren4 Department of Marine Ecosystems Dynamics, Atmosphere and Ocean Research Institute, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8564, Japan; Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan; Bavarian State Collection of Zoology, Munchhausenstr. 21, D-81247 Munich, Germany; and Swedish Museum of Natural History, Box 50007, SE-10405 Stockholm, Sweden

The egg capsules of neritid snails (Gastropoda: Neritimorpha) are made of a tough inner organic layer and an outer calcareous layer for further reinforcement. Such hard capsules are less susceptible to mechanical damage compared with soft or thin capsules of other gastropods, and there have been only a few reports of predation on neritid eggs. Here, we describe drilling predation on the reinforced egg capsule of Nerita japonica by Reishia clavigera (Caenogastropoda: Muricidae) on a high intertidal rocky shore in central Japan. The muricid makes a small, elliptical drill hole in the capsule lid by the use of both an accessory boring organ (ABO) and a radula, as it does in mollusc and barnacle shells. The etching around the hole by the acid secretion from the ABO, which can be observed under a dissecting microscope and by scanning electron microscopy, should provide an effective way to identify muricid predation on neritid eggs, probably not only by R. clavigera but also by other species in the warm temperate to tropical regions all over the world. Reishia clavigera made drill holes in c. 14% of the capsules, making it possibly the main cause of mortality for neritid eggs at the study site. However, this mortality rate is lower than those previously reported for caenogastropod eggs with softer capsules. All penetrated capsules of N. japonica were white (rather than brownish) and newly laid, suggesting that their acid-resistant organic layer had yet to harden at the time of radular rasping. The thick organic layer and calcareous coating are an effective armour, not only against the usual type of grazing but also against more sophisticated predation involving the chemical and mechanical boring of Muricidae.

Larval dispersal significantly contributes to the geographic distribution, population dynamics, and evolutionary processes of animals endemic to deep-sea hydrothermal vents. Little is known as to the extent that their larvae migrate vertically to shallower waters and experience stronger currents and richer food supplies. Here, we first provide evidence from early life-history traits and population genetics for the surface dispersal of a vent species. Planktotrophic larvae of a red blood limpet, Shinkailepas myojinensis (Gastropoda: Neritimorpha: Phenacolepadidae), were cultured to observe their swimming behavior and to evaluate the effects of temperature on survival and growth. In addition, the population structure was analyzed based on 1.2-kbp mitochondrial DNA sequences from 77 specimens that cover the geographic and bathymetric distributions of the species (northwest Pacific, 442-1,227 m in depth). Hatched larvae constantly swam upward at 16.6-44.2 mm/min depending on temperature. Vertical migration from hydrothermal vents to the surface, calculated to take ~4-43 d, is attainable given their lengthy survival time without feeding. Fed larvae best survived and grew at 25°C (followed by 20°C), which approximates the sea surface temperature in the geographic range of the species. Little or no growth was observed at the temperature of the vent habitat where adult limpets occur (≤15°C). Population genetic analyses showed no differentiation among localities that are

Despite the extraordinary morphological and ecological diversity of Neritimorpha, few studies have focused on the phylogenetic relationships of this lineage of gastropods, which includes four extant superfamilies: Neritopsoidea, Hydrocenoidea, Helicinoidea, and Neritoidea. Here, the nucleotide sequences of the complete mitochondrial genomes of Georissa bangueyensis (Hydrocenoidea), Neritina usnea (Neritoidea), and Pleuropoma jana (Helicinoidea) and the nearly complete mt genomes of Titiscania sp. (Neritopsoidea) and Theodoxus fluviatilis (Neritoidea) were determined. Phylogenetic reconstructions using probabilistic methods were based on mitochondrial (13 protein coding genes and two ribosomal rRNA genes), nuclear (partial 28S rRNA, 18S rRNA, actin, and histone H3 genes) and combined sequence data sets. All phylogenetic analyses except one converged on a single, highly supported tree in which Neritopsoidea was recovered as the sister group of a clade including Helicinoidea as the sister group of Hydrocenoidea and Neritoidea. This topology agrees with the fossil record and supports at least three independent invasions of land by neritimorph snails. The mitochondrial genomes of Titiscania sp., G. bangueyensis, N. usnea, and T. fluviatilis share the same gene organization previously described for Nerita mt genomes whereas that of P. jana has undergone major rearrangements. We sequenced about half of the mitochondrial genome of another species of Helicinoidea, Viana regina, and confirmed that this species shares the highly derived gene order of P. jana., This work was supported by the Spanish Ministry of Science and Innovation (CGL2010-18216 and CGL2013-45211-C2-2-P to RZ; BES-2011-051469 to JEU)

Euthyneuran gastropods represent one of the most diverse lineages in Mollusca (with over 30,000 species), play significant ecological roles in aquatic and terrestrial environments and affect many aspects of human life. However, our understanding of their evolutionary relationships remains incomplete due to missing data for key phylogenetic lineages. The present study integrates such a neglected, ancient snail family Ringiculidae into a molecular systematics of Euthyneura for the first time and is supplemented by the first microanatomical data. Surprisingly, both molecular and morphological features present compelling evidence for the common ancestry of ringiculid snails with the highly dissimilar Nudipleura—the most species-rich and well-known taxon of sea slugs (nudibranchs and pleurobranchoids). A new taxon name Ringipleura is proposed here for these long-lost sisters, as one of three major euthyneuran clades with late Palaeozoic origins, along with Acteonacea (Acteonoidea + Rissoelloidea) and Tectipleura (Euopisthobranchia + Panpulmonata). The early Euthyneura are suggested to be at least temporary burrowers with a characteristic ‘bubble’ shell, hypertrophied foot and headshield as exemplified by many extant subtaxa with an infaunal mode of life, while the expansion of the mantle might have triggered the explosive Mesozoic radiation of the clade into diverse ecological niches.

The Rissooidea is an evolutionarily ancient and mega-diverse group of marine micro-gastropods that occur from intertidal to deep waters at all latitudes. Their current systematics is predominantly based on phenetic grounds and there has been no comprehensive molecular phylogeny. Based on sequences of mitochondrial and nuclear DNA from the most complete sampling of Rissoidae to date, this work represents the first treatment of the group performed through a phylogenetic approach. The main goals are to clarify the phylogenetic position of the Rissoidae, investigate the relationships within rissoid taxa and test the utility of some diagnostic morphological traits. Our phylogeny indicates that the Rissoidae are one of six distinct family-lineages within the superfamily Rissooidea (along with Barleeiidae, Emblandidae, Lironobidae, Rissoinidae and Zebinidae) whose recognition is supported by several synapomorphies. While most of the characters studied exhibit widespread convergence, some others prove useful in separating genera and broader taxonomic groups. The relationships among rissoid taxa challenge the current systematics, indicating the non-monophyly of some genera with purportedly trans-oceanic distribution and the need of taxonomic revision for some highly diverse genera. Our phylogeny suggests that the Rissoidae originated in shallow seas and independently radiated into bathyal waters at least twice.

The nucleotide sequences of mitochondrial DNA fragments containing genes for cytochromecoxidase subunits I and II, ATPase subunits 6 and 8, large and small subunits of rRNA, and 9 tRNAs were determined using 2 genetically distinct representative specimens of the hydrothermal vent-endemic genus,Alviniconcha, and for the hydrothermal vent-endemic species,Ifremeria nautilei(Provannidae: Caenogastropoda: Mollusca). All 3 specimens showed tRNATrpgene translocation. To determine the time point at which this translocation occurred, we determined the nucleotide sequences of fragments containing 7 tRNA genes for another 3Alviniconchaand 2Ifremeriaspecimens, as well as for 7 related species. Our findings indicated that the translocation occurred in a common ancestor of theAlviniconchaandIfremeriagenera. Relatively long non-coding regions were observed on both sides of the tRNATrpgene and at the original position of this gene in all theAlviniconchaandIfremeriagastropod specimens. Overall, the mitochondrial non-coding regions appear to provide much more information about genetic structure than the mitochondrial COI gene does and could therefore be a valuable marker for future studies.

Intriguing fossils encrusting oncoids and exhumed carbonate concretions are described from the Middle Jurassic (Bathonian) of Poland. The fossils, up to a few millimeters in diameter and preserved in a form of calcium carbonate, are characterized by a tubular, elongate shape with the external surface covered with distinctive semicircular to oval concavities. These tubes do not match any known fossils and do not represent trace fossils sensu stricto. They are similar to serpulid and/or sabellid polychaetes with which they are associated. The latter, however, have calcitic tubes and none are known to possess the concave structures that characterize the tubular fossils. The shape of the concavities and the presence of a carbonate lining within them suggest that the tubular fossils were originally covered with ooids, a few of which are still preserved in the concavities. These Middle Jurassic fossils may represent the fossilized remnants of agglutinated tubes formed by polychaete worms. Their greatest abundances are noted on media bearing thick microbial crusts (oncoidal in nature) on which they often form dense aggregations. This may indicate that the tube-building worms selected such media not only because they provided a suitable hard surface for settlement, but also because they were a rich source of food in the form of both microbes (Cyanophyta) and other organic matter present in the microbial mats. The selectivity of only ooids for tube building makes them dissimilar to any known recent tube-building polychaetes and, thus, the Middle Jurassic representatives are nonactualistic with respect to particle selection for the tube formation.

Kano, Y., Kimura, S., Kimura, T. & Waren, A. (2012) Living Monoplacophora: morphological conservatism or recent diversification? —Zoologica Scripta, 41, 471–488. The molluscs of the class Monoplacophora are classic and probably the most striking case of a ‘living fossil’ in the deep sea. Until the discovery of the first living specimens in 1950s, the group was thought to be extinct since the Devonian period, almost 400 million years ago. Morphological conservatism over a long span of time in a ‘living-fossil’ lineage may theoretically result in distant but closely resembling taxa, and this idea apparently led some authors to recognise as many as six families and three superfamilies for less than three dozen living monoplacophoran species. However, no genetic or fossil data have been available regarding the history of their diversification. Here we describe Veleropilina seisuimaruae sp. n., the first member of the class from the north-western Pacific, based on the shell, radular and anatomical characteristics. Phylogenetic analyses of 6-kb DNA sequences estimate that the divergence of V. seisuimaruae and Laevipilina hyalina, the only other monoplacophoran available for genetic studies, dates back only to the Late Cretaceous, despite their significant morphological differences among the living members of the class. The recent Monoplacophora might have radiated fairly recently from a cryptic lineage with ordinary rates of morphological evolution, possibly after the global deep-sea anoxia at the Cenomanian/Turonian boundary.

The amphibious ‘bug-eating slug’ Aiteng ater Swennen & Buatip, 2009 shows a worm-like, compact body shape lacking any cephalic tentacles or body processes. Anatomically it has been described as showing an unusual mix of sacoglossan and acochlidian characters, thus the systematic affinities are uncertain. The species is redescribed here with an integrative microanatomical and molecular approach. All major organ systems were three-dimensionally reconstructed from serial histological sections using AMIRA software. Aiteng ater has a prepharyngeal nerve ring with separate cerebral and pleural ganglia rather than cerebro-pleural ganglia, and no sacoglossan-like ascus is detectable histologically. The radula is triseriate rather than uniseriate, showing one lateral tooth on each side of the rhachidian tooth. A well-developed two-chambered heart is present. The vas deferens in A. ater splits off distal to the female glands. The intestine is short and opens into a small mantle cavity. Long cavities in the connective tissue are remains of dissolved calcareous spicules. Only a few characters thus remain to support a closer relationship of A. ater to Sacoglossa, i.e. the Gascoignella-like body shape lacking cephalic tentacles, the presence of an elysiid-like system of dorsal vessels, and an albumen gland consisting of follicles. Additionally we describe in microanatomical detail an equally small and vermiform new aitengid species from Japan. Aiteng mysticus n. sp. differs from A. ater in habitat, body size and colour, central nervous system and presence of a kidney. Both aitengid species resemble acochlidians in the retractibility of the head, by possessing calcareous spicules, a prepharyngeal nerve ring with separated cerebral and pleural ganglia, a triseriate radula with an ascending and descending limb, but without sacoglossan-like ascus, and a special diaulic reproductive system. The prominent rhachidian tooth of Aitengidae, which is used to pierce insects and pupae in A. ater, and the large, laterally situated eyes closely resemble the anatomy of members of the limnic Acochlidiidae. The acochlidian nature of Aiteng is strongly indicated by our molecular analysis, in which it forms a basal hedylopsacean offshoot or the sister clade to limnic Acochlidiidae and brackish or marine Pseudunelidae within Hedylopsacea. Such a topology would, however, imply that Aitengidae have lost the most characteristic acochlidian apomorphy, the subdivision of the body into a headfoot complex and a free, elongated visceral hump. Also, the absence of cephalic tentacles gives the Aitengidae an appearance that is very different to other, strictly aquatic Acochlidia. Differences of the external morphology and the internal anatomy are discussed in the light of a habitat shift of Aitengidae within the Acochlidia.

Neritid snails (Gastropoda: Neritimorpha) protect their eggs in a hard capsule, of tough conchiolin, reinforced by mineral particles derived from the faeces and stored in a special sac near the anus and oviduct opening. Predation on this arguably hardest of molluscan egg capsule is described and illustrated here; neritids of the freshwater to brackish-water genera Clithon and Vittina, generally classified as herbivores, feed facultatively on the eggs of various confamilial species after breaking the reinforced capsule lid by means of prolonged radular rasping. Intensive predation pressure by these common inhabitants in Indo-West Pacific coastal streams may have given rise to the remarkable egg-laying behaviour of Neritina on the shells of other living snails. Our laboratory examination showed that Neritina species deposited clusters of egg capsules more frequently on the living shell than on other substrates, and that the predation rate was significantly lower on this moving ‘nursery’. Predation rate was even lower on the small egg capsules of Clithon and Vittina themselves, which were deposited one by one in the depressions on the rough surfaces of stones.

The helicoid microgastropod genera Leptogyra, Xyleptogyra and Leptogyropsis from deep, sunken wood off New Zealand, were originally classified among the poorly defined Skeneidae (Vetigastropoda, Trochoidea) based on shell characters, external morphology and fine-structure of radulae. We investigated the microanatomy and histology of several representatives by means of serial semi-thin sectioning followed by computer-aided 3D-reconstruction, studied the shell structure, and performed phylogenetic analyses of histone (H3) and COI-sequences in order to substantiate the neomphalidan nature of these genera. The anatomical data, in particular the lack of sensory papillae, the presence of a single left kidney, left-side innervated copulatory organs, glandular gonoducts, eggs without a vitelline layer, a single pair of radular cartilages, a rectum passing beneath the heart and statocysts with a single statolith clearly exclude Leptogyra, Xyleptogyra and Leptogyropsis from the Skeneidae and from the Vetigastropoda as a whole, but strongly suggest a systematic position among the Neomphalida, where the small, helicoid genus Melanodrymia shows most similarities. This conclusion is also supported by shell structure (in particular by the presence of shell pores similar to Neomphalus), and by the molecular trees. Similar to whale falls, the sunken wood habitat might have served as an ecological bridge between the ancestral regular deep benthos and the hydrothermal vent habitat otherwise typical for Neomphalida. We argue that Neomphalida is a separate basal clade of rhipidoglossate Gastropoda.