A comprehensive molecular phylogeny of the brachyuran crab superfamily Xanthoidea provides novel insights into its systematics and evolutionary history.

Maximum likelihood and Bayesian phylogenies for the brachyuran crab superfamily Xanthoidea were estimated based on three mitochondrial and four nuclear genes to infer phylogenetic relationships and inform taxonomy. Habitat data was then used in conjunction with several diversification rates analyses (BAMM, BiSSE, HiSSE, and FiSSE) to test evolutionary hypotheses regarding the diversification of xanthoid crabs. The phylogenies presented are the most comprehensive to date in terms of global diversity as they include all four constituent families (Xanthidae, Panopeidae, Pseudorhombilidae, and Linnaeoxanthidae) spanning all oceans in which xanthoid crabs occur. Six Xanthoidea families are recognised. Panopeidae and Xanthidae sensu stricto are the two largest family-level clades, which are reciprocally monophyletic. Pseudorhombilidae is nested within and is here treated as a subfamily of Panopeidae. Former subfamilies or tribes of Xanthidae sensu lato are basally positioned clades in Xanthoidea and are here assigned family-level ranks: Garthiellidae, Linnaeoxanthidae, Antrocarcinidae, and Nanocassiopidae. The genera Linnaeoxantho and Melybia were recovered in separate clades with Linnaeoxantho being sister to the family Antrocarcinidae, while Melybia was recovered within the family Panopeidae. The existing subfamily classification of Xanthidae and Panopeidae is drastically restructured with 20 xanthid and four panopeid subfamilies provisionally recognised. Diversification-time analyses inferred the origin of Xanthoidea and Garthiellidae in the Eocene, while the other families originated during the Oligocene. The majority of genus- and species-level diversification took place during the Miocene. Ancestral state reconstruction based on depth of occurrence (shallow vs. deep water) shows some ambiguity for the most recent common ancestor of Xanthoidea and Nanocassiopidae. The most recent common ancestors of Antrocarcinidae and Panopeidae were likely deep-water species, while those of Garthiellidae and Xanthidae were probably shallow-water species. Several shifts in net diversification rates were detected but they were not associated with depth-related habitat transitions.

Extraordinary majoid crabs: the genus Esopus A. Milne-Edwards, 1875 in the new subfamily Esopinae subfam. nov., and erection of Paulitinae subfam. nov. (Crustacea, Decapoda, Brachyura, Majoidea, Inachoididae Dana, 1851).

A rare small species, Esopus crassus A. Milne-Edwards, 1875, recently collected by KARUBENTHOS Expedition 2015 in Guadeloupe, is re-examined. The genus Esopus A. Milne-Edwards, 1875, currently included in the Epialtidae MacLeay, 1838, must be assigned to the Inachoididae Dana, 1851, a rather basal family within the Majoidea Samouelle, 1819, but deviates from the morphotype that is being traditionally associated to this group. It deserves its own subfamily, Esopinae subfam. nov., besides other inachoidid subfamilies, for which a description is here provided (Collodinae Stimpson, 1871; Dasygyiinae Holmes, 1900; Inachoidinae Dana, 1851; Salaciinae Dana, 1851; Stenorhynchinae Dana, 1851). Another inachoidid subfamily is erected here, Paulitinae subfam. nov., for the genus Paulita Guinot, 2012, monotypic with P. tuberculata (Lemos de Castro, 1949, as Dasygyius tuberculatus). A reliable fossil member is recorded from the lower Miocene onwards.

Diagnosis of the inachoidid subfamily Paradasygyiinae subfam. nov (Crustacea, Decapoda, Brachyura, Majoidea).

The name for the brachyuran subfamily Dasygyiinae Holmes, 1900, recently recognised by Guinot Van Bakel (2020) in the majoid family Inachoididae Dana, 1851, cannot be used as it is a junior synonym of Collodinae Stimpson, 1871. The present note diagnoses a new name, Paradasygyiinae subfam. nov., for the monotypic genus Paradasygyius Garth, 1958.

Reappraisal of species attributed to Halicarcinus White, 1846 (Crustacea: Decapoda: Brachyura: Hymenosomatidae) with diagnosis of four new genera and one new species from New Ireland, Papua New Guinea.

Species of Hymenosomatidae previously treated as species or junior synonyms of species of Halicarcinus White, 1846 are assigned to this and other genera. Halicarcinus is restricted to seven valid species; Rhynchoplax Stimpson, 1858, since 1980 synonymised with Halicarcinus, is now recognised with four species; four species are added to Micas Ng & Richer de Forges, 1996 (making five in total); and four new genera are erected: Culexisoma n. gen. (two species, one newly described), Lucascinus n. gen. (three species), Nasutoplax n. gen. (one species) and Stimpsoplax n. gen. (three species). The genera are distinguished primarily on features of the gonopod 1, interaction of the pleon with the thoracic sternal pleonal cavity, maxilliped 3, male cheliped, propodus-dactylus articulation of the ambulatory pereopods, and degree of fusion of the pleomeres. Species of Halicarcinus s.s. share a short trilobed rostrum, strongly curved gonopod 1 and free pleomeres. Some members of other genera may have a similar rostrum but typically have a long median projection with or without lateral angles or spines variously developed at the anterior margin of a supraocular eave. A lectotype of Hymenicus cookii Filhol, 1885 (now Halicarcinus cookii) is designated. A lectotype of Hymenosoma leachii Guérin, 1832, in Guérin-Méneville 1829-1837 (synonym of Halicarcinus planatus Fabricius, 1775) is selected in the interests of nomenclatural stability. Halicarcinus quoyi (H. Milne Edwards, 1853) is recognised as a senior synonym of the more widely used H. innominatus Richardson, 1949, which is itself a nomen nudum because it was erected without type designation. We also recognise Hymenicus marmoratus Chilton, 1882, as a junior synonym of Halicarcinus varius (Dana, 1851). Species of Rhynchoplax share a curved gonopod 1, falcate dactyli on pereopods 2-5 and fused pleomeres 3-4 in males and 3-5 in females. Species of Micas have a twisted gonopod 1 with the apex bent and only one or two subapical teeth on the dactylus of ambulatory legs. Culexisoma n. gen. is established for Halicarcinus ginowan Naruse & Komai, 2009, and a second species, Culexisoma niugini n. sp., from Papua New Guinea as type species. The genus is unique among these genera in having the male pleon not tightly engaging with the thoracic sternum, maxillipeds 3 not fully covering the buccal cavern and in having a strongly sexually dimorphic rostrum. Species of Lucascinus n. gen. share a male cheliped with 'nut-cracker'-like fingers and free pleomeres in both male and female. Nasutoplax n. gen. differs from others in the erect lateral profile of the rostrum and in gonopod 1 with an unusual subterminal spinulose projection on its posterior face. Stimpsoplax n. gen. has a gonopod 1 with a swollen base and a narrow strongly twisted distal part, tapering distally to a curved apex. Each genus is diagnosed, all species are tabulated, some discussed in more detail, and generic diagnostic characters are illustrated.

Correct date and authorship of taxa of Middle American freshwater crabs described by Rodríguez & Smalley (1972) (not 1969) and included in Smalley (1970) (Crustacea: Decapoda: Brachyura: Pseudothelphusidae).

One subgenus and one genus of Pseudothelphusidae described by Gilberto Rodríguez and Alfred E. Smalley from Mexico have been erroneously referred to for over 40 years as variously described in 1968 and 1969. The review of the original publication indicates that these taxa were published in a journal dated 1969 that became available for distribution only in 1972. Smalley (1970), who believed that the original manuscript had been previously published, referred to some of these new taxa (i.e., Epithelphusa, E. mixtepensis, Tehuana and T. veracruzana) and provided sufficient information to make these names available in 1970, thus becoming the correct authorship for these four taxa. Therefore they must be referred to as "Rodríguez & Smalley in Smalley 1970". A list of all affected taxa with the correct publication date and authorship is given. A list of publications in which the taxa authored by Rodríguez and Smalley were erroneously referred to as published in 1969 is also provided.

Significance of the sexual openings and supplementary structures on the phylogeny of brachyuran crabs (Crustacea, Decapoda, Brachyura), with new nomina for higher-ranked podotreme taxa.

The patterns of complexity of the male and female sexual openings in Brachyura, which have been the source of uncertainties and conflicting opinions, are documented, together with a study of the morphologies of the coxal and sternal gonopores in both sexes, penises, spermathecae, and gonopods. The vulvae, male gonopores and penises are described among selected taxa of Eubrachyura, and their function and evolution examined in the context of a wide variety of mating behaviours. The location of female and male gonopores, the condition of the penis (coxal and sternal openings and modalities of protection), and related configurations of thoracic sternites 7 and 8, which are modified by the intercalation of a wide sternal part (thoracic sternites 7 and 8) during carcinisation, show evidence of deep homology. They represent taxonomic criteria at all ranks of the family-series and may be used to test lineages. Of particular significance are the consequences of the posterior expansion of the thoracic sternum, which influences the condition, shape, and sclerotisation of the penis, and its emergence from coxal (heterotreme) to coxo-sternal, which is actually still coxal (heterotreme), in contrast to a sternal emergence (thoracotreme). The heterotreme-thoracotreme distinction results from two different trajectories of the vas deferens and its ejaculatory duct via the P5 coxa (Heterotremata) or through the thoracic sternum (Thoracotremata). Dissections of males of several families have demonstrated that this major difference not only affects the external surface (perforation of the coxa or the sternum by the ejaculatory duct) but also the internal anatomy. There is no evidence for an ejaculatory duct passing through the articular membrane between the P5 coxa and the thoracic sternum in any Brachyura, even when the sternal male gonopore is very close to the P5 coxa. Trends towards the coxo-sternal condition are exemplified by multistate characters, varying from a shallow depression to a long groove along expanded sternites 7 and 8, and ultimately their complete, extended junction typifying the most derived coxo-sternal condition. The coxo-sternal condition is indicative of a long evolutionary history, as evidenced by the presence of multistate characters (e.g., Dorippidae, Goneplacoidea) or by a single, well-established condition (e.g., Chasmocarcinidae, Ethusidae, Panopeidae Eucratopsinae, Rhizopidae, Scalopidiidae). The penial area proves to be an essential diagnostic feature in Brachyura, with a value comparable to that of the gonopods. Penis protection is ubiquitous in Brachyura irrespective of length, and several modalities of protection prevail, which necessitate different modifications of associated structures. A long penis in a gutter developed from a partial invagination of sternite 8 induces the formation of a new "suture" at the same level as the preceding suture 6/7. Such a "supplementary suture 7/8" exists among unrelated heterotreme families (e.g., Ethusidae, Panopeidae Eucratopsinae, Pseudorhombilidae, Rhizopidae). A fully protected penis, concealed in a groove within a complete invagination of sternite 8 in the form of two contiguous plates, evolved independently (homoplasy) in Palicoidea and Chasmocarcinidae (Goneplacoidea), with sternite 8 present as a single plate in females. In condylar protection, described for the first time and occurring in several heterotreme families, the penis emerges from the extremity of the P5 coxo-sternal condyle or from its anterior border instead of from the coxa itself. A penis precisely lodged in a small excavation on sternite 8, which is lined by a row of stiff setae, is unique to Brachyura, and represents a new synapomorphy of the Homoloidea. Five modalities of penis protection are recognised in Podotremata, eight in Eubrachyura (six in Heterotremata and two in Thoracotremata). Special attention has been paid to Dorippoidea (Dorippidae and Ethusidae), which shows transformation series from coxal to coxo-sternal conditions. The coxo-sternal condition is not an intermediate towards the thoracotreme organisation, and a step in heterotreme evolution is the adoption of the coxo-sternal condition. An extreme carcinisition may also result in the sternal arrangement of male gonopores in the form of a "sternitreme" disposition, as in the case of Hymenosomatoidea, which displays a broad thoracic sternum and true sternal male gonopores (as in thoracotremes) together with several plesiomorphic traits that are assumed to represent an old, deeply-rooted heterotreme clade. A sternitreme condition evolved independently in the most ancestral heterotreme clades (such as Hymenosomatoidea) and in Thoracotremata. The older the lineage of a heterotreme is, the higher the possibility of having evolved carcinisation. Evidence that "derived" traits may be the consequence of a strong carcinisation, rather than being recently acquired, necessitates reconsidering certain character states in Brachyura. Eubrachyurans can only evolve either the heterotreme or the thoracotreme arrangement, the consistency of the inferred ancestral characters states providing a useful criterion for evaluating ancestral trait reconstructions. A widened thoracic sternum together with sternal gonopores may be present in carcinised heterotremes such as hymenosomatoids. The thoracic sternum provides a reliable complex of characters that must be carefully interpreted. The hypothesis of a coxo-sternal disposition in Cryptochiroidea and Pinnotheroidea, generally considered thoracotremes, is rejected, and an alternative interpretation of their status is discussed. A new interpretation of the phylogeny of Cryptochiroidea is outlined, but the origin of Pinnotheroidea remains puzzling. The sella turcica, frequently regarded a synapomorphy of Eubrachyura, is redefined as the structure formed by the endosternal intertagmal phragma that connects the tagma/thorax and the tagma/abdomen to thoracic interosternite 7/8. It is here termed the "brachyuran sella turcica" and is shown to be synapomorphic to all Brachyura. The Eubrachyura synapomorphically shares the fusion of the thoracic interopleurite 7/8 with the brachyuran sella turcica, forming the "eubrachyuran sella turcica". In contrast, some Podotremata (Cyclodorippoidea and Raninoidea) share a connection between the sella turcica and the thoracic interosternite 6/7. Six main patterns of the thoracic sternum in relation to variations in sutures 4/5-7/8 are recognised in Eubrachyura, whereas several subpatterns that include variations in the median line are distinguished. The evolution of the thoracic sternum and axial skeleton is reassessed in Podotremata and Eubrachyura. A posteriormost location of the male gonopore (coxal or sternal) in relation to sternite 8 characterises many brachyurans (Cryptochiroidea, Hymenosomatoidea, Majoidea, Matutidae, Menippidae, Orithyioidea, Parthenopoidea, Ucididae, Grapsoidea--including Percnidae, Plagusiidae, Varunidae), in contrast to a location close to suture 7/8 in other groups. The thoracic sternum/pterygostome junction, which has multistate characters, is shown to be a valuable taxonomic criterion. The shapes of the sterno-abdominal depression and sterno-abdominal cavity provide diagnostic features that are helpful in suprageneric assignments. The monophyly of Brachyura, Eubrachyura, and Thoracotremata is reaffirmed. The monophyly of Brachyura is supported by the interdependence of the two pairs of gonopods and penis. An abdomen permanently flexed and held by the pereopods and/or the homoloid press button (on sternite 4) or typical eubrachyuran press-button (on sternite 5) may be considered a synapomorphy of Brachyura, the absence of this condition considered a loss. The double abdominal-locking system ("double peg") on sternite 5, a device discovered in three families of the extinct Palaeocorystoidea from the Upper Aptian, is similar to the double hook present in living lyreidids, although it is lost in all other raninoid extant members. New evidence shows that the abdominal holding was an early occurrence for a brachyuran crab. The Raninoidea, sister to Palaeocorystoidea, is characterised by gymnopleurity, a condition that results from the lifting of the carapace and thus the exposure of several pleurites. The narrowing of the body and thoracic sternum, almost certainly associated with their burrowing behaviour, is a diagnostic feature of raninoid evolution, in contrast to the widening observed in the remaining Brachyura. The monophyly of Heterotremata is discussed. Although the correct assignment of the coxal male gonopore and sternal female gonopore (vulva) at the base of Decapoda and Eubrachyura, respectively, left no synapomorphies to support the Heterotremata, the group nevertheless should be regarded as the sister group to Thoracotremata. The controversial monophyly of Podotremata is discussed and arguments are presented against the suppression of this taxon. The distinction of Homoloidia from Dromioidia is argued, and a classification of Podotremata, which considers the fossil record whenever possible, is presented. The earliest brachyurans are re-examined, and a new interpretation of the phylogeny of several basal eubrachyuran groups (Dorippoidea, Inachoididae, Palicoidea, Retroplumoidea) is proposed. Stenorhynchus shares a number of characters with the Inachoididae that differentiate them from Inachidae, and also has some distinctive features that warrants its assignment to a separate inachoidid subfamily, Stenorhynchinae, which is resurrected. The concealment strategies among Brachyura are documented and discussed. Podotremes use carrying behaviour, often combined with burying and concealment under substrates, whereas living within a host, burying, and decoration are used by heterotremes, burrowing being essentially a thoracotreme strategy.(ABSTRACT TRUNCATED)

Molecular systematics of the deep-sea hydrothermal vent endemic Brachyuran family Bythograeidae: a comparison of three Bayesian species tree methods.

Brachyuran crabs of the family Bythograeidae are endemic to deep-sea hydrothermal vents and represent one of the most successful groups of macroinvertebrates that have colonized this extreme environment. Occurring worldwide, the family includes six genera (Allograea, Austinograea, Bythograea, Cyanagraea, Gandalfus, and Segonzacia) and fourteen formally described species. To investigate their evolutionary relationships, we conducted Maximum Likelihood and Bayesian molecular phylogenetic analyses, based on DNA sequences from fragments of three mitochondrial genes (16S rDNA, Cytochrome oxidase I, and Cytochrome b) and three nuclear genes (28S rDNA, the sodium-potassium ATPase a-subunit 'NaK', and Histone H3A). We employed traditional concatenated (i.e., supermatrix) phylogenetic methods, as well as three recently developed Bayesian multilocus methods aimed at inferring species trees from potentially discordant gene trees. We found strong support for two main clades within Bythograeidae: one comprising the members of the genus Bythograea; and the other comprising the remaining genera. Relationships within each of these two clades were partially resolved. We compare our results with an earlier hypothesis on the phylogenetic relationships among bythograeid genera based on morphology. We also discuss the biogeography of the family in the light of our results. Our species tree analyses reveal differences in how each of the three methods weighs conflicting phylogenetic signal from different gene partitions and how limits on the number of outgroup taxa may affect the results.

Two new species of hydrothermal vent crabs of the genus Bythograea from the southern East Pacific Rise and from the Galapagos Rift (Crustacea Decapoda Brachyura Bythograeidae).

Two new species of Bythograea Williams, B. vrijenhoeki n. sp. and B. galapagensis n. sp., are described based on morphology and mitochondrial DNA comparisons. B. vrijenhoeki was collected on the southern East Pacific Rise, south of the Easter Microplate and B. galapagensis from the Galapagos Rift, from where B. intermedia de Saint Laurent was also described. Our analyses indicate that B. vrijenhoeki is the sister species of B. laubieri Guinot and Segonzac, and B. galapagensis is the sister species of B. thermydron Williams. Bythograea is now composed of six described species, all endemic to hydrothermal vents along the East Pacific Rise and from the Galapagos Rift.

New genus and species of brachyuran crab from the southern East Pacific Rise (Crustacea Decapoda Brachyura Bythograeidae).

A new genus and species of a brachyuran crab, Allograea tomentosa n. gen. and n. sp., of the family Bythograeidae, collected at a hydrothermal vent locality south of the Easter Microplate (31 degrees 09'S) on the southern East Pacific Rise, is described. The genus Allograea is distinguished by lacking modifications of the fronto-orbital region, and by the absence of coloured fields and setal patches on the carapace and chelipeds. The body and legs are smooth but densely covered by a brown tomentum, the eyestalks are not reduced, but the cornea is unfaceted and unpigmented. Comparison of mitochondrial DNA sequences among all known bythograeid genera confirms the novelty of this taxon.