Porcellanid crab Pachycheles stevensii parasitized by rhizocephalans Lernaeodiscus spp.: population biology in the northwestern Sea of Japan.

We examined the population and reproductive characteristics of the anomuran crab Pachycheles stevensii Stimpson, 1858 (Decapoda: Porcellanidae) heavily infested by 2 rhizocephalans of the genus Lernaeodiscus in the northern part of the species range (Peter the Great Bay, Sea of Japan) in 2020-2021. The prevalence of infestation reached 32.3%, and L. rybakovi proved to be much more numerous than L. kasyanovi. The sex structure of the P. stevensii population was represented by males (38.8%), females (50.6%), and modified specimens (10.6%), which were extremely feminized males. The latter had a broadened abdomen, smaller chelae, shortened gonopod, and 3 additional pairs of female-type pleopods. Thus, the initial sex ratio in the P. stevensii population approximated the expected 1:1, as in most porcellanid crabs. No significant modifications of the secondary sex characters of the female hosts were observed. The size structures of males and females did not significantly differ. P. stevensii produced 1 clutch yr-1. Oviposition and incubation lasted from summer to early fall; recruitment was noted in the fall. There was a correlation between the reproductive cycles of the host and parasites: rhizocephalans with mature externae were found from June-October. A large number of ovigerous female P. stevensii simultaneously carried parasitic externae of L. rybakovi; fecundity was considerably higher in non-infested females.

Functional morphology of the primary olfactory centers in the brain of the hermit crab Coenobita clypeatus (Anomala, Coenobitidae).

Terrestrial hermit crabs of the genus Coenobita display strong behavioral responses to volatile odors and are attracted by chemical cues of various potential food sources. Several aspects of their sense of aerial olfaction have been explored in recent years including behavioral aspects and structure of their peripheral and central olfactory pathway. Here, we use classical histological methods and immunohistochemistry against the neuropeptides orcokinin and allatostatin as well as synaptic proteins and serotonin to provide insights into the functional organization of their primary olfactory centers in the brain, the paired olfactory lobes. Our results show that orcokinin is present in the axons of olfactory sensory neurons, which target the olfactory lobe. Orcokinin is also present in a population of local olfactory interneurons, which may relay lateral inhibition across the array of olfactory glomeruli within the lobes. Extensive lateral connections of the glomeruli were also visualized using the histological silver impregnation method according to Holmes-Blest. This technique also revealed the structural organization of the output pathway of the olfactory system, the olfactory projection neurons, the axons of which target the lateral protocerebrum. Within the lobes, the course of their axons seems to be reorganized in an axon-sorting zone before they exit the system. Together with previous results, we combine our findings into a model on the functional organization of the olfactory system in these animals.

First Finding of Representatives of the Eccrinida Order in the Digestive Tract of King Crab Specie from the Barents Sea.

This is the first report on the finding of large intra-intestinal symbionts belonging to the order Eccrinida in crab-like decapod crustaceans of the family Lithodidae, Paralithodes camtschaticus and Lithodes maja, inhabiting the Barents Sea. Studies have been regularly conducted since the early 2000s in Kola Bay and in one of the inlets of the Eastern Murman Coast. Since 2005, Eccrinida representatives (presumably, a new species of the genus Arundinula) have been found in the guts of the red king crab. A brief description of the endosymbionts and data on their frequency of occurrence are presented. The possible reasons for the distribution of eccrinids in the crab-like decapod crustaceans of the Barents Sea are discussed.

A new species of Munidopsis from a seamount of the Southwest Indian Ocean Ridge (Decapoda: Munidopsidae).

Wood and whale bone colonisation experiments were undertaken on the Southwest Indian Ocean Ridge, 18 November 2009. Later, 14 December 2011, squat lobsters were recovered from the submerged wood and assigned to Munidopsis sp. Further study indicated that the specimens belonged to the group of species having a rostrum without lateral spines, presence of two strong epigastric spines, unarmed abdominal segments, one dorsal eye-spine, and with the second pereiopod not reaching the end of the first. They were similar to M. hemingi Alcock & Anderson, 1899 but differed in that the epigastric spines are well developed (vs. tubercles in M. hemingi), the lateral margins of the carapace are straight (vs. more convex in M. hemingi), the eye has a tubercular process mediodorsally (vs. a papilliform spinule at mesial angle) and the epipods on the fourth pereiopod were absent (vs. present in M. hemingi). Consequently the Munidopsis specimens from the Southwest Indian Ocean Ridge were considered to be an undescribed species.

A new Munidopsis species (Galatheoidea, Munidopsidae) from the Southwestern Atlantic.

Six Munidopsis species are recorded to the Southwestern Atlantic: M. barbarae; M. erinacea; M. nitida; M. sigsbei; M. riveroi and M. transtridens. Herein a new Munidopsis species from Southwestern Atlantic is described: Munidopsis trindadensis sp.nov., was sampled off Trindade Island (Espírito Santo, Brazil) at 360 m depth and differs from all six species previously recorded in this region by the telson with seven plates.

Squat lobsters (Crustacea: Anomura) from Mauritanian waters (West Africa), with the description of a new species of Munidopsis.

This paper is the result of the study of a squat lobsters collection obtained along the Mauritanian coast, between 91 and 1867 m depth, during the 'MAURIT' surveys carried out in the period from 2007 to 2010. Eumunida bella de Saint Laurent & Macpherson, 1990 (Chirostyloidea) and six species of Munida and Munidopsis (Galatheoidea) are reported in the present work.A new species, Munidopsis anaramosae n. sp. collected off northwestern Banc d'Arguin at 1000-1012 m depth, is described and illustrated. The presence of an eyespine that arises distally from the middle end of the cornea, walking legs merus spinose on dorsal and ventral margins and cheliped merus ventrally unarmed distinguish it from related species. Munida chunii Balss, 1913 is redescribed here and the new records of Munida guineae Miyake & Baba, 1970, M. speciosa von Martens, 1878 and Munidopsis chunii Balss, 1913 extend their geographical distribution northwards, and in the case of the last species, increase its bathymetric range.

Taxonomic study of the Pagurus forbesii "complex" (Crustacea: Decapoda: Paguridae). Description of Pagurus pseudosculptimanus sp. nov. from Alborán Sea (Southern Spain, Western Mediterranean Sea).

Study of hermit crabs from Alboran Sea has allowed recognition of two different morphological forms under what had been understood as Pagurus forbesii. Based on morphological observations with various species of Pagurus, and molecular studies, a new species is described as P. pseudosculptimanus. An overview of species of Pagurus from the eastern Atlantic and Mediterranean Sea is provided.

Just a matter of size? Evaluating allometry and intersexual heterometry in Pagurus bernhardus using ratios and indices (Decapoda, Anomura).

Heterochely denotes the presence of dissimilarly sized chelipeds on opposite sides of the body, a prevalent occurrence in diverse crustaceans. Conversely, heterometry pertains to the quantifiable disparities in size between these chelipeds. Both chelipeds hold pivotal roles in activities such as foraging, mating, and defense. Consequently, individuals of both genders in heterochelic species exhibit this morphological pattern. Previous studies have identified sexual dimorphism in cheliped size, with males displaying larger major chelipeds compared to females, albeit solely relying on propodus length as a size proxy and focusing solely on the major cheliped. In our study, we meticulously examined 190 specimens of the common European hermit crab Pagurus bernhardus from two collections. We sought to elucidate allometric relationships and assess whether heterometry exhibited sex-based differences when adjusting for body size by using ratios. Our findings revealed that male chelipeds displayed hyperallometric growth relative to females, and all three calculated heterometry indices exhibited significant disparities between the sexes. Consequently, male specimens exhibited larger major and minor chelipeds, even when theoretically matched for body size with females. This phenomenon may be attributed, among other factors, to male-male contests. Should indirect mate selection favor males with larger chelipeds in proportion to their body size, this dynamic could potentiate sexual selection in their favor.

Phylogenetic synthesis of morphological and molecular data reveals insights on the classification of diogenid hermit crabs (Crustacea: Decapoda: Anomura).

The family Diogenidae Ortmann, 1892 is a diverse and abundance group of hermit crabs, but their systematics and phylogenetic relationships are highly complex and unresolved. Herein, we gathered nucleotide sequence data from two mitochondrial (16S rRNA and COI) and two nuclear (NaK and PEPCK) genes for a total of 2,308 bp in length across 38 species from six extant diogenid genera. Molecular data were combined with 41 morphological characters to estimate the largest phylogeny of diogenid hermit crabs to date with the aim of testing the proposed taxonomic scheme of Diogenidae and addressing intergeneric relationships within this family. Despite conflicts between mitochondrial and nuclear DNA trees, the combined-data tree reflects the contributions of each dataset, and improves tree resolution and support for internal nodes. Contrary to traditional classification, our total evidence revealed a paraphyletic Diogenidae based on internally nested representatives of Coenobitidae Dana, 1851. Within Diogenidae, the studied diogenid hermit crabs were split between two clades with high support, which contradicts recent morphological classification scheme for Diogenidae sensu lato based on fossil records. The genus Diogenes Dana, 1851 was found nested inside Paguristes Dana, 1851, which formed a clade being separated from the remainder, pointing towards paraphyly in Paguristes. In another clade, Dardanus Paulson, 1875 occupied a basal position relative to the other diogenids, while Calcinus Dana, 1851 and Clibanarius Dana, 1852 showed sister relationships and formed a cluster with Ciliopagurus Forest, 1995. Among the morphological characters examined, carapace shield and telson were identified as phylogenetically significant for grouping diogenid genera, while phylogenetic insignificance of gill number was evidenced by its mosaic pattern in diogenid phylogeny. The present study sheds light on the controversial generic phylogeny of Diogenidae and highlights the necessity for thorough taxonomic revisions of this family as well as some genera (e.g., Paguristes) to reconcile current classifications with phylogenetic relationships.

Morphological diversity in true and false crabs reveals the plesiomorphy of the megalopa phase.

Brachyura and Anomala (or Anomura), also referred to as true and false crabs, form the species-rich and globally abundant group of Meiura, an ingroup of Decapoda. The evolutionary success of both groups is sometimes attributed to the process of carcinization (evolving a crab-like body), but might also be connected to the megalopa, a specific transitional larval phase. We investigate these questions, using outline analysis of the shields (carapaces) of more than 1500 meiuran crabs. We compare the morphological diversity of different developmental phases of major ingroups of true and false crabs. We find that morphological diversity of adults is larger in false crabs than in true crabs, indicating that taxonomic diversity and morphological diversity are not necessarily linked. The increasing morphological disparity of adults of true and false crabs with increasing phylogenetic distance furthermore indicates diverging evolution of the shield morphology of adult representatives of Meiura. Larvae of true crabs also show larger diversity than their adult counterparts, highlighting the importance of larvae for biodiversity studies. The megalopa phase of Meiura appears to be plesiomorphic, as it overlaps between true and false crabs and shows little diversity. Causes may be common evolutionary constraints on a developmental phase specialized for transitioning.

Nervous systems in 3D: a comparison of Caridean, anomuran, and brachyuran zoea-I (Decapoda).

Using serial semi-thin sections and digital 3D-reconstructions we studied the nervous systems of zoea-I larvae in three decapod species, Hippolyte inermis (Leach, 1815), Porcellana platycheles (Pennant, 1777), and Pachygrapsus marmoratus (Fabricius, 1787). These taxa represent three decapod lineages, that is, Caridea, Anomura, and Brachyura, each characterized by specific zoea-I morphology. Special attention was paid to development of ganglia, neuropil composition, and segmental nerves. In all zoeae studied, the overall elements, for example, the segmental ganglia, their neuropils and most of the nerves of the adult decapod nervous system are present. Ongoing differentiation processes are observable as well, most obvious in segments with well-developed limbs the ganglia are in a more advanced stage of differentiation and more voluminous compared to segments with only limb buds or without externally visible limb anlagen. Intra- and interspecific comparisons indicate that neuromere differentiation thus deviates from a simple anterior-posterior gradient as, for example, posterior thoracic neuromeres are less developed than those of the pleon. In addition, the differences in the progress of the development of ganglia between the studied taxa can best be attributed to heterochronic mechanisms. Taxon and stage-specific morphologies indicate that neuronal architecture reflects both, morphogenesis to the adult stage and specific larval adaptions, and provides sets of characters relevant to understanding the corresponding phylogeny.

A new species of the hermit crab genus Diogenes (Crustacea: Decapoda: Anomura: Diogenidae) from southern India.

A new species of the hermit crab genus Diogenes Dana, 1851 (Diogenidae), D. canaliculatus, is described and illustrated on the basis of material from off the Kerala State, southern India. It is referred to the D. edwardsii (De Haan, 1849) species group, and compared with D. bicristimanus Alcock, 1905, D. fasciatus Rahayu & Forest, 1995, D. laevicarpus Rahayu, 1996 and D. moosai Rahayu & Forest, 1995. The characteristically sculptured left chela and the unarmed dorsal margins of the propodi of the second and third pereopods distinguish the new species from these congeners.

Munidopsis kareenae, a new species of seamount squat lobster from New Zealand with a key to the New Zealand species of Munidopsis (Crustacea: Decapoda: Munidopsidae).

A new species of the squat lobster genus Munidopsis is described from Nukuhou Seamount, North Island, New Zealand. The new species is allied to members of the "Galathodes group" within Munidopsis that share a flattened, distally trifid rostrum, an unarmed carapace surface (apart from paired epigastric spines in some species), unarmed abdominal tergites and absence of pereopodal epipods. The new species is readily separated from these species by the combination of unarmed lateral carapace margins posterior to the anterolateral spine, absence of epigastric spines, and prominently spinose extensor margins of the pereopod 2-4 meri. Fourteen species of Munidopsis are now recorded from New Zealand; a key to the New Zealand species is provided.

Records of the hermit crab genus Pagurixus Melin, 1939 (Crustacea: Decapoda: Anomura: Paguridae) from Europa Island, Western Indian Ocean, with descriptions of two new species.

Three species of the pagurid hermit crab genus Pagurixus Melin, 1939, are reported from Europa Island in the Mozambique Strait, western Indian Ocean: P. haigae Komai & Osawa, 2007, P. annulus n. sp., and P. europa n. sp. Pagurixus haigae is recorded from the western Indian Ocean for the first time. Pagurixus annulus n. sp. and P. europa n. sp. are referred to the P. boninensis (Melin, 1939) species group and P. anceps (Forest, 1954) group, respectively. Diagnostic characters of these two new species are discussed.

Redescription and taxonomic status of Paguristes weddellii (H. Milne Edwards) (Crustacea: Anomura: Paguroidea: Diogenidae) from the eastern Pacific.

The type and additional material of Paguristes weddellii (H. Milne Edwards, 1848) were examined. The species is redescribed and illustrated in details. Comparison of P. weddellii with the monotypic genus Tetralobistes Ayón-Parente & Hendrickx, 2010b, shows many similarities, principally in the armature of the distal margin of the male first pleopod and the shape of the telson, which in both cases feature a tetralobular posterior margin, a character considered unique among the Diogenidae. Consequently, Pagurus weddellii is transfered to the genus Tetralobistes. Paguristes hirtus Dana, 1851, a subjective junior synonym of Pagurus weddellii is removed from the synonymy based on lack of direct evidences.

New species and new records of deepwater munidid squat lobsters from north-western Australia: Onconida, Bathymunida, Crosnierita, Plesionida and Torbenella.

Seven species of Munididae are reported from the continental margin of north-western Australia. Three species are new to science: Crosnierita adela sp. nov., Onconida ariel sp. nov. and Plesionida aurelia sp. nov., each presently known only from Western Australia. Four species are reported for the first time from Australian waters, Bathymunida balssi Van Dam, 1838, Bathymunida dissimilis Baba & de Saint Laurent, 1996, Crosnierita yante (Macpherson, 1994) and Torbenella orbis (Baba, 2005). Keys to the world species of the genera represented are provided.

A new species of deep-sea squat lobster of the genus Munida Leach, 1820 (Crustacea: Decapoda: Anomura: Munididae) from a hydrothermal field in the southwestern Indian Ocean.

A new species of the genus Munida Leach, 1820, is described and illustrated based on a single specimen from the deep-sea hydrothermal area in the southwestern Indian Ocean. Munida manqingae sp. nov. closely resembles M. tiresias Macpherson 1994, but differs in the morphology of the carapace, basal segment of the antennular peduncles, first segment of the antennal peduncle.

Rediscovery and range extension of Ciliopagurus liui Forest, 1995 and description of a new species of Pagurus Fabricius, 1775 (Crustacea: Decapoda: Anomura: Paguroidea) from the Kerala State, southwestern India.

Two species of paguroid hermit crabs, Ciliopagurus liui Forest, 1995 (Diogenidae) and Pagurus spinossior n. sp. (Paguridae), are reported from the Kerala State, southwestern India. Ciliopagurus liui, is first recorded from the Indian Ocean. This species was originally described on the basis of a single male specimen from the Tonkin Gulf in the South China Sea, though its geographical range also included Japan, based on literature. Supplemental description and illustrations are provided for better understanding of the diagnostic features of this little known species. Pagurus spinossior n. sp., described on the basis of a single male specimen, appears closest to P. spinulentus (Henderson, 1888), known only by the holotype from the Philippines, but the lack of spinules on the dorsal margins of the dactyli of the second pereopods, the different shape of the anterior lobe of the thoracic stemite 6, and the more numerous spines on the terminal to posterior margins of the telson distinguish the new species from P. spinulentus.

A new genus and some new species of the genus Lauriea Baba, 1971 (Crustacea, Decapoda, Galatheidae) from the Pacific and Indian Oceans, using molecular and morphological characters.

The genus Lauriea belongs to the family Galatheidae and is easily differentiated from other genera of the family by the endopod of the uropod being much wider than long and the dactyli of the walking legs being curved and strongly biunguiculate. Examination of many specimens collected during recent expeditions from Madagascar to French Polynesia and using morphological and molecular data revealed the existence of six species, five of them new, that are genetically distinct yet morphologically very similar. Furthermore, another new species, having a triunguiculate P2-4 dactyli, represents a new genus, Triodonthea.

Additional records of the pagurid hermit crab genus Trichopagurus de Saint Laurent, 1968 (Crustacea: Decapoda: Anomura), with description of a new species from the Philippines.

The pagurid hermit crab genus Trichopagurus de Saint Laurent, 1968 is currently represented by three shallow water spe- cies from the tropical Indo-West Pacific region. In this paper, three species of the genus, including one new species, are reported. Trichopagurus tenuidactylus n. sp. is described on the basis of a single ovigerous female from the Bohol Sea, the Philippines, and compared with two close relatives, T. asper Komai & Poupin, 2012 and T. macrochela Komai & Os- awa, 2005. New locality records are provided for T. macrochela (the Philippines) and T. trichophthalinus (Forest, 1954) (Taiwan and Marianas). An identification key to the four species of the genus is presented.