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Certain parasites can manipulate their hosts to enhance their own fitness and transmission success. Rhizocephalan barnacles are a notable example, inducing significant changes in their crustacean host's morphology, physiology, and behaviour. Until recently, it was believed that the spider crab Scyra aff. ferox is parasitized by a single species Sacculina pilosella in the Sea of Japan. However, previous molecular studies have revealed a complex of unrelated species, Sacculina pugettiae (fam. Sacculinidae) and Parasacculina pilosella (fam. Polyascidae). These rhizocephalans can even parasitize one host specimen simultaneously. Here, we investigated the interaction of S. pugettiae and P. pilosella with the nervous system of their common host. Species were identified based on receptacle morphology, with further validation through 18S gene phylogenetic analysis. The parasites interacted differently with the host nervous system: S. pugettiae had goblet‐shaped organs in the ganglion periphery, while P. pilosella lacked these structures, instead possessing numerous neuropil rootlets. In case of simultaneous infection, both goblet‐shaped organs and neuropil rootlets were present. Histochemistry revealed the presence of muscular rosettes in the rootlets of both species, suggesting a similar organization of the muscular system despite phylogenetic differences. Scanning electron microscopy confirmed the presence of host cell projections enveloping the rootlets. This study provides insights into the morphological features of rhizocephalan‐decapod interaction and highlights differences in their interaction with host nervous tissue between families. Our results also confirmed the loss of the goblet‐shaped organs in Polyascidae. [ABSTRACT FROM AUTHOR]

The results of this study showed that out of 287 individuals (135 males and 152 females) of the spider crab Menaethius monoceros collected from the Red Sea and the Gulfs of Suez and Aqaba, 15 individuals (6 males and 9 females) were infected with Parasacculina pilosella (Van Kampen & Boschma, 1925) (Polyascidae: Rhizocephala: Cirripedia: Crustacea). A total of 20 externae were recorded, including 11 singles, three doubles, and only one triple on the infected crab abdomens. The overall infection rate was 5.23% for the combined sexes at all sites, declined to 4.44% in males, but increased to 5.92% in females, reaching a higher rate of 16.07% in the populations of Marsa Alam and Shalateen sectors during summer. The examined externae have variable colors, sizes, and shapes based on their sexual maturity, which has been classified into four stages: immature or virgin, early mature, maturing, and late (spent externae). The largest number of externae was eight extruded on the 3rd abdominal segment, while it decreased to six, two, and one on the 4th, 2nd and 5th segments, respectively. The size of externae varied from 1.3 × 1.0 × 1.0 to 6.3 × 4.5 × 2.5 mm (Breadth × Height × Thickness). These results showed changes in the external secondary sexual characters of the infected males, represented by the remarkable broadness of the abdomen fringed with marginal setae and invagination of the sternum, but were limited in infected females.

The results of this study showed that out of 287 individuals (135 males and 152 females) of the spider crab Menaethius monoceros collected from the Red Sea and the Gulfs of Suez and Aqaba, 15 individuals (6 males and 9 females) were infected with Parasacculina pilosella (Van Kampen & Boschma, 1925) (Polyascidae: Rhizocephala: Cirripedia: Crustacea). A total of 20 externae were recorded, including 11 singles, three doubles, and only one triple on the infected crab abdomens. The overall infection rate was 5.23% for the combined sexes at all sites, declined to 4.44% in males, but increased to 5.92% in females, reaching a higher rate of 16.07% in the populations of Marsa Alam and Shalateen sectors during summer. The examined externae have variable colors, sizes, and shapes based on their sexual maturity, which has been classified into four stages: immature or virgin, early mature, maturing, and late (spent externae). The largest number of externae was eight extruded on the 3rd abdominal segment, while it decreased to six, two, and one on the 4th, 2nd and 5th segments, respectively. The size of externae varied from 1.3 × 1.0 × 1.0 to 6.3 × 4.5 × 2.5 mm (Breadth × Height × Thickness). These results showed changes in the external secondary sexual characters of the infected males, represented by the remarkable broadness of the abdomen fringed with marginal setae and invagination of the sternum, but were limited in infected females. [ABSTRACT FROM AUTHOR]

Introduction: This study undertakes a detailed examination of the host range and distribution patterns of Rhizocephala, a group of specialized parasitic barnacles, within Korean marine environments. It aims to expand the understanding of their biodiversity and ecological impact. Methods: Employing both morphological observation and mitochondrial DNA sequencing, the study identifies the variety of rhizocephalan species infecting decapod hosts in Korean waters, aiming to document their diversity and distribution. Results: The investigation identifies 26 rhizocephalan species parasitizing 28 decapod hosts, including the discovery of three new parasite-host relationships not previously reported. It was observed that while a few rhizocephalan species infect multiple hosts, most have a narrow host range. Additionally, the study maps out regional differences in Rhizocephala diversity across three Korean marine ecoregions, noting the highest diversity in the warmer East China Sea ecoregion and lower diversity in the colder Yellow Sea and East Sea ecoregions. Discussion: The findings underscore the necessity for continued taxonomic research on Rhizocephala and their host species to better understand and manage these parasites, which hold significant ecological and economic importance. The study suggests that geographical variations in host-parasite relationships are influenced by regional climatic conditions, particularly winter water temperatures. [ABSTRACT FROM AUTHOR]

Background. Rhizocephalan interaction with their decapod hosts is a superb example of host manipulation. These parasites are able to alter the host's physiology and behavior. Host-parasite interaction is performed, presumably, via special modified rootlets invading the ventral ganglions. Methods. In this study, we focus on the morphology and ultrastructure of these special rootlets in Polyascus polygeneus (Lützen & Takahashi, 1997), family Polyascidae, invading the neuropil of the host's nervous tissue. The ventral ganglionic mass of the infected crabs were fixed, and the observed sites of the host-parasite interplay were studied using transmission electron microscopy, immunolabeling and confocal microscopy. Results. The goblet-shaped organs present in the basal families of parasitic barnacles were presumably lost in a common ancestor of Polyascidae and crown "Akentrogonida", but the observed invasive rootlets appear to perform similar functions, including the synthesis of various substances which are transferred to the host's nervous tissue. Invasive rootlets significantly differ from trophic ones in cell layer composition and cuticle thickness. Numerous multilamellar bodies are present in the rootlets indicating the intrinsic cell rearrangement. The invasive rootlets of P. polygeneus are enlaced by the thin projections of glial cells. Thus, glial cells can be both the first hosts' respondents to the nervous tissue damage and the mediator of the rhizocephalan interaction with the nervous cells. One of the potential molecules engaged in the relationships of P. polygeneus and its host is serotonin, a neurotransmitter which is found exclusively in the invasive rootlets but not in trophic ones. Serotonin participates in different biological pathways in metazoans including the regulation of aggression in crustaceans, which is reduced in infected crabs. We conclude that rootlets associated with the host's nervous tissue are crucial for the regulation of host-parasite interplay and for evolution of the Rhizocephala. [ABSTRACT FROM AUTHOR]

Background Rhizocephalan interaction with their decapod hosts is a superb example of host manipulation. These parasites are able to alter the host’s physiology and behavior. Host-parasite interaction is performed, presumably, via special modified rootlets invading the ventral ganglions. Methods In this study, we focus on the morphology and ultrastructure of these special rootlets in Polyascus polygeneus (Lützen & Takahashi, 1997), family Polyascidae, invading the neuropil of the host’s nervous tissue. The ventral ganglionic mass of the infected crabs were fixed, and the observed sites of the host-parasite interplay were studied using transmission electron microscopy, immunolabeling and confocal microscopy. Results The goblet-shaped organs present in the basal families of parasitic barnacles were presumably lost in a common ancestor of Polyascidae and crown “Akentrogonida”, but the observed invasive rootlets appear to perform similar functions, including the synthesis of various substances which are transferred to the host’s nervous tissue. Invasive rootlets significantly differ from trophic ones in cell layer composition and cuticle thickness. Numerous multilamellar bodies are present in the rootlets indicating the intrinsic cell rearrangement. The invasive rootlets of P. polygeneus are enlaced by the thin projections of glial cells. Thus, glial cells can be both the first hosts’ respondents to the nervous tissue damage and the mediator of the rhizocephalan interaction with the nervous cells. One of the potential molecules engaged in the relationships of P. polygeneus and its host is serotonin, a neurotransmitter which is found exclusively in the invasive rootlets but not in trophic ones. Serotonin participates in different biological pathways in metazoans including the regulation of aggression in crustaceans, which is reduced in infected crabs. We conclude that rootlets associated with the host’s nervous tissue are crucial for the regulation of host-parasite interplay and for evolution of the Rhizocephala.

Parasitic barnacles (Thecostraca: Rhizocephala) are among the most striking parasitic manipulators in the animal kingdom. "Kentrogonid" rhizocephalans significantly alter the physiology and behaviour of brachyuran crabs, while "akentrogonid" influence on hosts remains poorly studied. The specialised rootlets invading the nervous system that are presumably crucial for the host-parasite interplay were described in basal rhizocephalan families that display a kentrogonid life cycle. In this study, we present a histological description of such rootlets in the "akentrogonid" Diplothylacus sinensis (Keppen, 1877) (family Thompsoniidae) in the ventral nervous ganglia of the crab Portunus pelagicus (Linnaeus, 1758). The morphology of these rootlets varies greatly in cuticle structure, gross organisation of the rootlet tissues and presence/absence of large vacuoles. It is assumed that rootlet modification appears during its development and successive growth from the penetration site into the ganglia's neuropil. The absence of the goblet-shaped organs in D. sinensis supports the hypothesis that these structures were secondarily lost in the crown lineages of the Rhizocephala. • Diplothylacus sinensis has an abundant net of rootlets invading hosts nervous system • Rootlets of D. sinensis are not modified into goblet-shaped organs • Rootlets of D. sinensis have diverse types of tissue organisation • Crown groups of rhizocephalans presumably have lost goblet-shaped organs [ABSTRACT FROM AUTHOR]

Background: Rhizocephalan barnacles stand out in the diverse world of metazoan parasites. The body of a rhizocephalan female is modified beyond revealing any recognizable morphological features, consisting of the interna, a system of rootlets, and the externa, a sac-like reproductive body. Moreover, rhizocephalans have an outstanding ability to control their hosts, literally turning them into “zombies”. Despite all these amazing traits, there are no genomic or transcriptomic data about any Rhizocephala. Methods: We collected transcriptomes from four body parts of an adult female rhizocephalan Peltogaster reticulata: the externa, and the main, growing, and thoracic parts of the interna. We used all prepared data for the de novo assembly of the reference transcriptome. Next, a set of encoded proteins was determined, the expression levels of protein-coding genes in different parts of the parasite’s body were calculated and lists of enriched bioprocesses were identified. We also in silico identified and analyzed sets of potential excretory / secretory proteins. Finally, we applied phylostratigraphy and evolutionary transcriptomics approaches to our data. Results: The assembled reference transcriptome included transcripts of 12,620 protein-coding genes and was the first for any rhizocephalan. Based on the results obtained, the spatial heterogeneity of protein-coding gene expression in different regions of the adult female body of P. reticulata was established. The results of both transcriptomic analysis and histological studies indicated the presence of germ-like cells in the lumen of the interna. The potential molecular basis of the interaction between the nervous system of the host and the parasite's interna was also determined. Given the prolonged expression of development-associated genes, we suggest that rhizocephalans “got stuck in their metamorphosis”, even at the reproductive stage. Conclusions: The results of the first comparative transcriptomic analysis for Rhizocephala not only clarified but also expanded the existing ideas about the biology of these extraordinary parasites.

Sex allocation theory predicts the adaptive allocation of resources to male versus female reproduction in simultaneous hermaphrodites in response to individual characteristics or environmental factors. Because parasites uptake resources from their hosts, their presence could affect the sex allocation of the hosts. We investigated the effects of infestation status and infestation intensity by the rhizocephalan barnacle Boschmaella japonica on reproduction, including sex allocation, of the host intertidal barnacle Chthamalus challengeri. Feeding activity was also examined as a factor related to resource intake. Both male and female reproductive investment decreased with increasing parasite infestation, and the sex allocation of large infested hosts was more male-biased than that of large uninfested hosts. Moreover, in contrast to the model prediction that male investment does not change under resource limitation, male investment decreased in infested hosts whose resources were taken by parasites. This reduction in male investment could be explained by changes in mating group size, since infested hosts have shorter penises and consequently are able to access fewer mating partners., (© The Author(s) 2025. Published by Oxford University Press on behalf of the European Society of Evolutionary Biology.)

Los cangrejos del género Callinectes están ampliamente distribuidos en aguas cálidas. Habitan principalmente en lagunas costeras y estuarios. En las lagunas del golfo de México, están sujetos a una pesquería importante. En el caso de México, Callinectes sapidus y Callinectes rathbunae contribuyen con 90 % de la captura nacional. Un aspecto importante en el ciclo de vida de los cangrejos es el parasitismo causado por balanos parásitos del orden Rhizocephala, debido a su alta prevalencia y periodicidad. El objetivo del presente estudio fue proveer de información reciente acerca del número de externas por individuo en cangrejos de la especie C. rathbunae. En un muestreo comercial realizado en marzo de 2019, se capturaron tres especímenes de la especie C. rathbunae parasitados con el balano rizocéfalo Loxothylacus texanus: un ejemplar macho con dos externas vírgenes, una hembra con cinco externas vírgenes, y un organismo macho con cinco externas maduras. Este es el primer reporte en donde se presenta evidencia de cinco externas en un hospedero, se concluyó que esta prevalencia fue baja. Es importante realizar más estudios de este tipo para comprender del todo el ciclo de vida de L. texanus y su impacto en las poblaciones de sus hospederos.

Background: Rhizocephalan barnacles stand out in the diverse world of metazoan parasites. The body of a rhizocephalan female is modified beyond revealing any recognizable morphological features, consisting of the interna, a system of rootlets, and the externa, a sac-like reproductive body. Moreover, rhizocephalans have an outstanding ability to control their hosts, literally turning them into “zombies”. Despite all these amazing traits, there are no genomic or transcriptomic data about any Rhizocephala. Methods: We collected transcriptomes from four body parts of an adult female rhizocephalan Peltogaster reticulata: the externa, and the main, growing, and thoracic parts of the interna. We used all prepared data for the de novo assembly of the reference transcriptome. Next, a set of encoded proteins was determined, the expression levels of protein-coding genes in different parts of the parasite’s body were calculated and lists of enriched bioprocesses were identified. We also in silico identified and analyzed sets of potential excretory / secretory proteins. Finally, we applied phylostratigraphy and evolutionary transcriptomics approaches to our data. Results: The assembled reference transcriptome included transcripts of 12,620 protein-coding genes and was the first for any rhizocephalan. Based on the results obtained, the spatial heterogeneity of protein-coding gene expression in different regions of the adult female body of P. reticulata was established. The results of both transcriptomic analysis and histological studies indicated the presence of germ-like cells in the lumen of the interna. The potential molecular basis of the interaction between the nervous system of the host and the parasite's interna was also determined. Given the prolonged expression of development-associated genes, we suggest that rhizocephalans “got stuck in their metamorphosis”, even at the reproductive stage. Conclusions: The results of the first comparative transcriptomic analysis for Rhizocephala not only clarified but also expanded the existing ideas about the biology of these extraordinary parasites.

The endoparasitic crustacean Sacculina carcini (Cirripedia: Rhizocephala) has a much simpler morphology than conventional filter-feeding barnacles, reflecting its parasitic lifestyle. To investigate the molecular basis of its refined developmental program, we produced a draft genome sequence for comparison with the genomes of nonparasitic barnacles and characterized the transcriptomes of internal and external tissues. The comparison of clusters of orthologous genes revealed the depletion of multiple gene families but also several unanticipated expansions compared to non-parasitic crustaceans. Transcriptomic analyses comparing interna and externa tissues revealed an unexpected variation of gene expression between rootlets sampled around host midgut and thoracic ganglia. Genes associated with lipid uptake were strongly expressed by the internal tissues. We identified candidate genes probably involved in host manipulation (suppression of ecdysis and gonad development) including those encoding crustacean neurohormones and the juvenile hormone binding protein. The evolution of Rhizocephala therefore appears to have involved a rapid turnover of genes (losses and expansions) as well as the fine tuning of gene expression. [ABSTRACT FROM AUTHOR]

Background: Rhizocephalan barnacles stand out in the diverse world of metazoan parasites. The body of a rhizocephalan female is modified beyond revealing any recognizable morphological features, consisting of the interna, the system of rootlets, and the externa, a sac-like reproductive body. Moreover, rhizocephalans have an outstanding ability to control their hosts, literally turning them into “zombies”. Despite all these amazing traits, there is no genomic and transcriptomic data about any Rhizocephala. Methods: We collected transcriptomes from four body parts of an adult female rhizocephalan Peltogaster reticulata: externa and main, growing, and thoracic parts of the interna. We used all prepared data for the de novo assembly of the reference transcriptome. Next, a set of encoded proteins was determined, the expression levels of protein-coding genes in different parts of the parasite body were calculated and lists of enriched bioprocesses were identified. We also in silico identified and analyzed sets of potential excretory / secretory proteins. Finally, we applied phylostratigraphy and evolutionary transcriptomics approaches to our data. Results: The assembled reference transcriptome included transcripts of 12,620 protein-coding genes and was the first for both P. reticulata and Rhizocephala. Based on the results obtained, the spatial heterogeneity of protein-coding genes expression in different regions of P. reticulata adult female body was established. The results of both transcriptomic analysis and histological studies indicated the presence of germ-like cells in the lumen of the interna. The potential molecular basis of the interaction between the nervous system of the host and the parasite's interna was also determined. Given the prolonged expression of development-associated genes, we suggest that rhizocephalans “got stuck in the metamorphosis”, even in their reproductive stage. Conclusions: The results of the first comparative transcriptomic analysis for Rhizocephala not only clarified but also expanded the existing ideas about the biology of this amazing parasites.

Rhizocephala is a group of highly modified parasitic crustaceans. The body of an adult female is formed de novo, and lacks most traits of free-living crustaceans. Despite the large number of studies dedicated to different aspects of rhizocephalan biology, the structure of the interna of these parasites is still poorly understood. The muscular systems specifically were described only for representatives of three families. The aim of our study is to visualize and describe the muscular system in the interna of Peltogasterella gracilis from the family Peltogasterellidae. P. gracilis has a colonial type of organization, with a common part of the interna and numerous externa-bearing modules. Interestingly, the muscular system has dissimilar organization in different parts of the interna. Muscular system in modules resembles that of Peltogaster paguri , while in the common part of the interna it's more similar to the muscular system of sacculinids and polyascids. We propose that the muscular system of rhizocephalans is a new structure in terms of evolution, and as such can be easily modified in respect to the functional characteristics of the different interna's parts. [ABSTRACT FROM AUTHOR]

Background: Rhizocephalan barnacles stand out in the diverse world of metazoan parasites. The body of a rhizocephalan female is modified beyond revealing any recognizable morphological features, consisting of the interna, the system of rootlets, and the externa, a sac-like reproductive body. Moreover, rhizocephalans have an outstanding ability to control their hosts, literally turning them into “zombies”. Despite all these amazing traits, there is no genomic and transcriptomic data about any Rhizocephala. Methods: We collected transcriptomes from four body parts of an adult female rhizocephalan Peltogaster reticulata: externa and main, growing, and thoracic parts of the interna. We used all prepared data for the de novo assembly of the reference transcriptome. Next, a set of encoded proteins was determined, the expression levels of protein-coding genes in different parts of the parasite body were calculated and lists of enriched bioprocesses were identified. We also in silico identified and analyzed sets of potential excretory / secretory proteins. Finally, we applied phylostratigraphy and evolutionary transcriptomics approaches to our data. Results: The assembled reference transcriptome included transcripts of 12,620 protein-coding genes and was the first for both P. reticulata and Rhizocephala. Based on the results obtained, the spatial heterogeneity of protein-coding genes expression in different regions of P. reticulata adult female body was established. The results of both transcriptomic analysis and histological studies indicated the presence of germ-like cells in the lumen of the interna. The potential molecular basis of the interaction between the nervous system of the host and the parasite's interna was also determined. Given the prolonged expression of development-associated genes, we suggest that rhizocephalans “got stuck in the metamorphosis”, even in their reproductive stage. Conclusions: The results of the first comparative transcriptomic analysis for Rhizocephala not only clarified but also expanded the existing ideas about the biology of this amazing parasites.

We studied the population and reproductive characteristics of the stone crab Hapalogaster dentata (De Haan, 1849) (Anomura: Lithodidae) parasitized by Briarosaccus hoegi (Rhizocephala: Peltogastridae) from Peter the Great Bay (northwestern Sea of Japan) in 2023. The sex structure of the H. dentata population was female-biased and represented by 39.1% males and 60.9% females. The size-frequency distribution differed between males and females. The prevalence of parasitization of H. dentata by B. hoegi reached 6.7%. No relationship between crab sex and parasitization prevalence was found. Most of the parasitized specimens (94.8%) had only a single parasitic externa. The non-parasitized and parasitized crabs did not differ in main carapace length. The pleopods in most of the externa-bearing females were shortened or completely atrophied. H. dentata produced 1 clutch per year with ovigerous females occurring from October to May. An obvious delay in embryonic development was observed in winter. None of the parasitized H. dentata females were ovigerous. Externae with embryos of B. hoegi were found from May to July.

This study is concerned with determining the infection rates of the hermit crab of the family Diogenidae, living off the southern coast of the Crimean Peninsula, Black Sea, with representatives of the superorder Rhizocephala. Individuals of the hermit crab, Diogenes pugilator were identified as being invaded by the specific parasite, Septosaccus cuenoti, with the invasion extensity (prevalence) and intensity at 10.6% and 0–2 individuals, respectively. It examines the morphology of the external part of the female parasite, and the externa, as well as eggs developing inside it. The embryonic development of the egg was found to occur in four stages. Calculations performed for each growth stage include the major and minor diameters of the egg; the shape index, and area and volume; the number of eggs with the developing embryos in the externa; the potential number of nauplii hatched by the female Septosaccus cuenoti per generation; and the estimated share of their yield from the initial number of fertilized oocytes. [ABSTRACT FROM AUTHOR]

By shuffling biogeographical distributions, biological invasions can both disrupt long‐standing associations between hosts and parasites and establish new ones. This creates natural experiments with which to study the ecology and evolution of host–parasite interactions. In estuaries of the Gulf of Mexico, the white‐fingered mud crab (Rhithropanopeus harrisii) is infected by a native parasitic barnacle, Loxothylacus panopaei (Rhizocephala), which manipulates host physiology and behaviour. In the 1960s, L. panopaei was introduced to the Chesapeake Bay and has since expanded along the southeastern Atlantic coast, while host populations in the northeast have so far been spared. We use this system to test the host's transcriptomic response to parasitic infection and investigate how this response varies with the parasite's invasion history, comparing populations representing (i) long‐term sympatry between host and parasite, (ii) new associations where the parasite has invaded during the last 60 years and (iii) naïve hosts without prior exposure. A comparison of parasitized and control crabs revealed a core response, with widespread downregulation of transcripts involved in immunity and moulting. The transcriptional response differed between hosts from the parasite's native range and where it is absent, consistent with previous observations of increased susceptibility in populations lacking exposure to the parasite. Crabs from the parasite's introduced range, where prevalence is highest, displayed the most dissimilar response, possibly reflecting immune priming. These results provide molecular evidence for parasitic manipulation of host phenotype and the role of gene regulation in mediating host–parasite interactions. [ABSTRACT FROM AUTHOR]

This review is devoted to the pelagic larvae of rhizocephalan crustaceans with a kentrogonid type of development (Thecostraca: Cirripedia: Rhizocephala). These barnacles have undergone such a significant reduction of adult stages connected with the parasitic lifestyle that only the presence of a nauplius larva in their development indicates that this unique group belongs to crustaceans. The main attention is paid to the morphological characters of the larvae that can be used in the taxonomy and phylogeny of Rhizocephala. The differences between the larvae of peltogastrid and sacculinid types are discussed. The sexual dimorphism of cyprids associated with different functions of male and female larvae is analyzed. [ABSTRACT FROM AUTHOR]

In dynamic systems, organisms are faced with variable selective forces that may impose trade-offs. In estuaries, salinity is a strong driver of organismal diversity, while parasites shape species distributions and demography. We tested for trade-offs between low-salinity stress and parasitism in an invasive castrating parasite and its mud crab host along salinity gradients of two North Carolina rivers. We performed field surveys every six to eight weeks over 3 years to determine factors influencing parasite prevalence, host abundance, and associated taxa diversity. We also looked for signatures of low-salinity stress in the host by examining its response (time-to-right and gene expression) to salinity. We found salinity and temperature significantly affected parasite prevalence, with low-salinity sites (less than 10 practical salinity units (PSU)) lacking infection, and populations in moderate salinities at warmer temperatures reaching prevalence as high as 60%. Host abundance was negatively associated with parasite prevalence. Host gene expression was plastic to acclimation salinity, but several osmoregulatory and immune-related genes demonstrated source-dependent salinity response. We identified a genetic marker that was strongly associated with salinity against a backdrop of no neutral genetic structure, suggesting possible selection on standing variation. Our study illuminates how selective trade-offs in naturally dynamic systems may shape host evolutionary ecology. [ABSTRACT FROM AUTHOR]

The externae of parasitic sacculind, Sacculina leptodiae (Sacculindae: Rhizocephala: Cirripedia) on the xanthid crab, Leptodius exaratus (Xanthidae: Brachyura) were recorded during this study. A total of 691 individuals (400 males and 291 females) of this crab were collected from the intertidal coasts of the Egyptian Red Sea, Gulf of Suez and Gulf of Aqaba, of them 38 (23 males and 15 females) were infected with this parasite. The overall infection rate recorded 5.50% for all populations and was slightly higher in males (5.75%) than in females (5.15%). It showed seasonal, spatial and sex variations, recorded the highest rate (7.91%) at Gulf of Suez, declined sharply to 3.85 % at Gulf of Aqaba, and 2.43 % at all populations of the Red Sea, recorded the minimum rate of 0.57% at the southern populations. Autumn has the highest rate (10.34 %) at Hurghada (northern Red Sea), followed by summer with 9.34 % and 7.69 % at the Gulf of Suez and Ras Mohammed (Northern Red Sea), respectively, declined to 2.94 % in summer at Gulf of Aqaba, but increased again to 5.56% during spring. A total of 41 externae were recorded on the infected individuals, comprised 35 individuals with single externa (92.11 %), and only three with double externe (7.89 %). The highest number of externae was 13 (31.70 %) occurred on the 6th abdominal segment, followed by 11 (26.82 %) on the 5th segments, declined to 1-5 on the other segments except the first. The size of externae varied from 1.0 to 10.4 mm in breadth, averaged 5.19± 2.76 mm in males and 5.63± 3.17 mm in females. The rootlets of internae of the parasite invaded ovaries, testes, hepatopancreas, and all spaces within the crab body cavities. The disappearance or destruction of testes in infected males accompanied by remarkable broadness and segmentation of abdomens fringed with dense and length setae lead to “Parasitic castration”, compared with a hyperfiminzation in infected females due to the destruction of undeveloped ovaries and increasing abdominal setae dense and length. [ABSTRACT FROM AUTHOR]

Rhizocephala is a group of endoparasitic barnacles, the morphological characteristics of which are degenerated, and which has recently undergone active molecular identification. Despite several recent studies of Korean rhizocephalans, a comprehensive analysis of rhizocephalan fauna has not yet been conducted. In this study, we analyzed morphological and molecular characteristics of 64 rhizocephalan samples from 15 decapod hosts sampled across the Korean coast. We found 16 Rhizocephala species of six genera from four Rhizocephala families, i.e. , Peltogasterellidae, Peltogastridae, Polyascidae, and Sacculinidae. Combining morphological examination and molecular analysis of mitochondrial cytochrome c oxidase I revealed three new species candidates, i.e. , Peltogasterella sp., Peltogaster sp., and Parasacculina sp. 1, and three rhizocephalans that have expanded their distribution range to the Korean coast, i.e. , Parasacculina oblonga , Sacculina angulata , and Sacculina gracilis , whose expanded their distribution range to Korean coast. A synthetic update of Korean Rhizocephala fauna including a species checklist and remarks regarding distribution and taxonomy is also presented.

Rhizocephalan barnacles are a unique group of endoparasitic crustaceans. In their extreme adaptation to endoparasitism, rhizocephalan adults have lost almost all features of their free-living relatives but acquired an outstanding degree of control over the body of their hosts (mostly decapods). The subtle influence exercised by rhizocephalans on the physiology, morphology and behaviour of their hosts is a vivid example of the most intimate host-parasite interactions but their mechanisms are very poorly known. In this study we examined the morphology and the adaptive ultrastructure of the organs invading the nervous system of the host in two rhizocephalan species from the families Peltogastridae, (Peltogaster paguri) and Peltogasterellidae (Peltogasterella gracilis). We found two essentially different types of structures involved in interactions of these two rhizocephalans with the nervous system of their hosts: modified rhizocephalan rootlets lying inside the ganglia and the neural fibres of the host enlacing the trophic rootlets of the parasites. We suggest that both these structures may be highly specialized tools allowing the parasite to interact with the host on the humoral level via neuromediators, hormones, attractants and trophic factors. [ABSTRACT FROM AUTHOR]

The reproduction and parasite associates of the squat lobster Munidopsis platirostris (A. Milne Edwards and Bouvier, 1894) were investigated based on collections made in the Bahamas and Curaçao with grassmat and bundled fishing net traps used to collect sipunculan worms and other small invertebrates. Size of ovigerous M. platirostris was significantly correlated with clutch size for females from both localities but females from the Bahamas produced significantly more eggs (on average 10.1 eggs/clutch) than females from Curaçao (on average 6.6 eggs/clutch). Early embryos of M. platirostris from the Bahamas were 0.74–0.82 mm in diameter, similar to some other species of Munidopsidae as well as Chirostylidae. Two species of crustaceans, another squat lobster and a leptostracan, as well as a limpet mollusc, were collected with M. platirostris in the Bahamas, while a sipunculan was an associated species in a Curaçao collection. One specimen of M. platirostris had an unidentified cryptoniscoid epicaridean isopod, possibly representing a new genus and species. Two specimens of M. platirostris each had one rhizocephalan externa of a species belonging to Lernaeodiscus Müller, 1862 but their morphology does not match that of L. schmitti Reinhard, 1950, the only species in the genus known from squat lobsters in the western Atlantic. Additional materials and tools, such as DNA analysis, are needed to describe these potentially new parasites and we suggest that use of these traps may be an effective method to obtain additional samples. [ABSTRACT FROM AUTHOR]

Parasitic barnacles, the Rhizocephala, infect and castrate their crustacean hosts, causing changes in host morphology, physiology, and behavior. The physiological processes by which rhizocephalans manipulate their hosts are not well understood. We used an untargeted LC-MS metabolomics approach to compare the metabolite profiles (e.g. small molecules such as signaling molecules and other products of metabolism) of lithodid crabs with and without rhizocephalan infections. We tested whether metabolite changes caused by rhizocephalan infection could be detected in the hemolymph, muscle, and hepatopancreas of the red king crab Paralithodes camtschaticus (Tilesius, 1815) and the hemolymph of the golden king crab Lithodes aequispinus Benedict, 1895 infected by the rhizocephalans Briarosaccus regalis Noever, Olson & Glenner, 2016 and B. auratum Noever, Olson & Glenner, 2016, respectively. Tissue and hemolymph samples were collected from both species of king crabs between 2013 and 2015 in southeast Alaska. Hundreds of potential metabolites were identified in all analyzed tissues, yet few differed with crab sex and no metabolites could differentiate infected and healthy crabs, regardless of sex. There were large variations in the crab metabolome according to collection year and location, which likely masked differences related to sex and infection status. This environmental-metabolomics approach suggests that the crab metabolome may be greatly influenced by environmental variation. Future studies in a more controlled environment will be necessary to further unravel how the host crab metabolome changes with rhizocephalan infection. [ABSTRACT FROM AUTHOR]

Coral reefs harbour an immense diversity of species, many of which live in association with one or more host organisms. Stony corals (Scleractinia) have been documented to host nearly 900 organisms, of which > 310 are decapod crustaceans. This associated fauna is also involuntary host to a diverse parasite fauna. Coral-dwelling gall crabs (Cryptochiridae) are obligate symbionts of scleractinian corals; however, records of their parasites are scarce, with only two named epicaridean isopod species known. Fieldwork focused on cryptochirids in the Indo-West Pacific and Caribbean yielded diverse new collections of both hosts and parasites. This new material was compared with material deposited in museum collections. Both previously described species were encountered in the newly collected material, as well as a new genus and species of bopyrid, a new genus and species of cryptoniscoid, four new species of Danalia, and the first record of a rhizocephalan parasitizing a gall crab, which is also described as a new species. Parasitism of gall crabs is more widespread than what could be assumed based on literature records, and all parasite species appear to be specific to hosts in this crab family. This is the first review of hypersymbioses between stony corals, gall crabs and the crabs' parasites and hyperparasites. [ABSTRACT FROM AUTHOR]

A sacculinid rhizocephalan parasite, Sacculina lata Boschma, 1933, was discovered in the Beibu Gulf (= Gulf of Tonkin) west of Hainan Island, China, occurring in 7.4% of 363 Charybdis miles (De Haan, 1835) collected by 30 trawls in July 2017. This is the first time that S. lata has been recorded in Beibu Gulf and in the Chinese Exclusive Economic Zones (EEZs). Of the sampled crabs from 9 stations, 8 males and 19 females were found bearing externae of S. lata on the abdomen, a prevalence of 4.1 and 11.2% in male and female crabs, respectively. The dominant size group of infected males was larger than that of females. There was no significant relationship between water depth and infection rate of the parasite. A positive correlation was found both between volume and weight of externae, and between surface area of externae and abdomen width of the host crabs. Carapace width and wet weight of infected crabs were significantly less than those of uninfected crabs. In male crabs, the first pleopods of infected individuals were shorter than normal, but their pleons were wider. The propodus of the chela of a parasitized crab was significantly larger than that of normal crabs, both in males and females. No rhizocephalan-infected female crab was found bearing eggs. [ABSTRACT FROM AUTHOR]

Rhizocephalan parasites have a peculiar life cycle, and their adults lost almost all traits found usually in Crustacea. Despite some data on anatomy and ultrastructure of interna of Peltogastridae, some crucial aspects of morphology are still unknown. For example, there is only one mentioning of myocytes found in interna of Rhizocephalans ( Sacculina carcini ). So we aimed at studying the muscular system of the interna of Peltogaster paguri using serial histological sectioning and fluorescent staining (TRITC-labeled phalloidin) with confocal microscopy. Within the wall of the main trunk we found striated muscular fibers. The majority of these fibers form a unidirectional single spiral. There are additional small fibers that connect the coils of the large spiral. The density of muscular fibers is highest near the externa stalk, and the number of muscle fibers decreases towards the distal part of the main trunk. We suggest that such a muscular system could provide peristaltic movements of the main trunk and the transport of nutrients through the interna. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cancer-like neoplasma was found in the interna of parasitic barnacle. • Tumor is located in the spherical widening of the interna's rootlets. • Tumor has disrupted tissue organization. • The tumor seems to originate from the floating cell lineage. Cancer-like neoplasms are extremely rarely present in arthropods, particularly in crustaceans. Thus, it is assumed that these animals have some efficient cancer-preventing mechanisms. However, several cases of cancer-like neoplasms are described in crustaceans, though only for the Decapoda. We identified a tumor in the parasitic barnacle Peltogaster paguri (Cirripedia: Rhizocephala), and described its histological structure. A spherical cell mass consisting mostly of roundish cells with big translucent nuclei, prominent nucleoli, and sparse chromatin, and of cells with condensed chromosomes, was found in the main trunk of the P. paguri rootlet system. Numerous mitoses were observed in this area. Such tissue organization is utterly uncharacteristic of the Rhizocephala. Based on acquired histological data, we assume that this tumor is a cancer-like neoplasm. This is the first report of a tumor identified in the rhizocephalans, as well as in non-decapod crustaceans as a whole. [ABSTRACT FROM AUTHOR]

One of the most conspicuous traits of parasitic organisms is a well-developed reproductive system. In Rhizocephala ("Crustacea": Cirripedia) it is believed to be nested in the externa-a "reproductive part" located outside of the host. However, it is not clear how nutrients are transported to the externa. Several authors described a system of lacunae in the externa, and muscular contractions probably enable transport through these cavities. The aim of our study was to visualize (using microcomputed tomography and confocal laser scanning microscopy) and describe lacunar and muscular systems in the externa of Peltogasterella gracilis (fam. Peltogasterellidae). The lacunar system consists of "ventral" lacuna and several protrusions. The "ventral" lacuna is probably responsible for visceral mass nutrition, and mantle protrusions are associated with the mantle nutrition. The gross organization of the muscular system mostly corresponds to previous descriptions in other rhizocephalan species. Nonetheless, we observed several features of the externa morphology that had not been described before such as a muscular thickening in the proximal externa's part and a stalk plug disk. The muscular thickening might play a role of a propulsatory organ, helping to transport liquid through the lacunar system. The plug disk might fill the hole in the host's cuticle after the old externa drop off. The results allow us to make first assumptions on transport mechanisms in Rhizocephala., (© 2023 Wiley Periodicals LLC.)

The swimming crabCharybdis longicollis, native to the western Indian Ocean, was first recorded in the Mediterranean in 1954. It is now established from Egypt to Greece, and dominates the sandy-mud bottoms at 25–80 m in the southeastern Mediterranean. The success ofC. longicollisis attributed to its high fecundity, agonistic behaviour and omnivorous diet, as well as the rise in seawater temperature. Since the early 1990s its populations in Israel and Turkey have been heavily parasitized by the alien rhizocephalanHeterosaccus dollfusi, which impacts its host’s behaviour, growth and fecundity, and causes mortality. Yet, 60 years after its first record in the Mediterranean, the population ofC. longicollisseems durable, and has recently spread to the lower shelf and upper slope off Israel, where it is common at 80 m and is found down to 250 m, greatly increasing its spatial spread. The maximal percentage of parasitization was 87.2%, 88.8%, 75.5% and 81.8% at depths of 40, 60, 80, 100 m, respectively, and 50% at 120 and 250 m. Here, we hypothesize on the possible contribution of the depletion of its putative fish predators, mainly rays, to the prevalence ofC. longicollison the lower shelf. [ABSTRACT FROM PUBLISHER]

Rhizocephalan barnacles in the genus Briarosaccus parasitize and castrate king crab hosts, thereby preventing host reproduction and potentially altering host abundance. To better understand how environmental factors in Alaska may influence Briarosaccus prevalence, we studied the effects of temperature and salinity on the larvae of Briarosaccus regalis (previously Briarosaccus callosus). Nauplius larvae were reared at 7 temperatures (2 to 16 C) and 8 salinities (19 to 40) to determine larval survival and development rates. Maximum survival occurred from 4 to 12 C and at salinities between 25 and 34. In the Gulf of Alaska and Bering Sea, ocean temperatures and salinities are often within these ranges; thus current conditions appear favorable for high B. regalis larval survival. In addition, temperature was negatively correlated with larval development time; thus warmer waters can reduce the time larvae are exposed to the dangers of the planktonic environment. Since only female B. regalis larvae can infect crabs, we investigated the sex ratios of B. regalis broods at different temperatures and how size and morphological traits can be used to sex cyprid larvae. Larval rearing temperature did not affect brood sex ratio ( F0.947, P = 0.369), but sex ratio varied among broods ( F221.9; P < 0.001). Male larvae (424.5 ± 24.3 μm [mean ± 1 SD]) were significantly larger than female larvae (387.6 ± 22.7 μm [mean ± 1 SD]; F1,221.4; P < 0.001), consistent with other rhizocephalan cyprids, but sizes overlapped between the sexes such that morphological traits were also necessary for determining sex. Overall, this study provides new information on the larval biology, larval morphology, and environmental tolerances of B. regalis, an important king crab parasite. [ABSTRACT FROM AUTHOR]

The article presents a study which examined the collected cirripedes or barnacles of the superorders of Thoracica, Acrothoracica and Rhizocepha. Information on the marine habitat, geographic distribution, morphology and biology, and anatomy of species collected is presented. The sampling methods of collecting rhizophelans from their hosts and larvae, prepraring the samples for microscopy and estimating heat stress of intertidal barnacles are described.

Specimens of the commercially important crab Portunus sanguinolentus (Herbst, 1783) were collected monthly in Honghai Bay, P. R. China and examined for the presence of two barnacles: the Lepadomorpha Octolasmis bullata (Aurivillius, 1894) and the Rhizocephala Diplothylacus sinensis (Keppen, 1877). O. bullata was observed in the branchial chambers and prevalence of their infestation varied in the monthly collections. High prevalence occurred in the time from June to August and from October to February. The mean intensity of O. bullata was 23.33 ± 18.91 barnacles per infested host, showing higher intensity in larger crabs. The parasite D. sinensis was observed on host surfaces with extemae or scars, and their prevalence was high in winter and low in summer. Crabs parasitized by D. sinensis showed a heavier fouling by O. bullata than the non-parasitized crabs. Larger crabs were more vulnerable to the infestation of O. bullata and the parasitism of D. sinensis. Thus, interaction of O. bullata and D. sinensis may cause synergistic effects on the host's health. Due to the great economic importance of the crab, attention should be paid to this relationship. [ABSTRACT FROM AUTHOR]

Parasitic barnacles (Cirripedia: Rhizocephala) are highly specialized parasites of crustaceans. Instead of an alimentary tract for feeding they utilize a system of roots, which infiltrates the body of their hosts to absorb nutrients. Using X-ray micro computer tomography (MicroCT) and computer-aided 3D-reconstruction, we document the spatial organization of this root system, the interna, inside the intact host and also demonstrate its use for morphological examinations of the parasites reproductive part, the externa. This is the first 3D visualization of the unique root system of the Rhizocephala in situ, showing how it is related to the inner organs of the host. We investigated the interna from different parasitic barnacles of the family Peltogastridae, which are parasitic on anomuran crustaceans. Rhizocephalan parasites of pagurid hermit crabs and lithodid crabs were analysed in this study. [ABSTRACT FROM AUTHOR]

Rhizocephalan barnacles have been reported to parasitize a wide range of king crab species ( Lithodidae). So far all these parasites have been assigned to a single species, Briarosaccus callosus Boschma, 1930, which is assumed to have a global distribution. Here we investigate Briarosaccus specimens from three different king crab hosts from the fjord systems of Southeastern Alaska: Lithodes aequispinus Benedict, 1895, Paralithodes camtschaticus ( Tilesius, 1815), and Paralithodes platypus ( Brandt, 1850). Using molecular markers and by morphological comparison we show that Briarosaccus specimens from these three commercial exploited king crabs are in fact morphologically distinct from B. callosus, and further represent two separate species which we describe. The two new species, Briarosaccus auratum n. sp. and B. regalis n. sp., are cryptic by morphological means and were identified as distinct species by the use of genetic markers ( COI and 16 S). They occur sympatrically, yet no overlap in king crab hosts occurs, with B. auratum n. sp. only found on L. aequispinus, and B. regalis n. sp. as parasite of the two Paralithodes hosts. © 2015 The Authors. Zoological Journal of the Linnean Society published by John Wiley & Sons Ltd on behalf of The Linnean Society of London [ABSTRACT FROM AUTHOR]