On the marine sister groups of the freshwater crabs (Crustacea: Decapoda: Brachyura)

Freshwater crab sister group relationships with marine eubrachyuran families were investigated. A morphology-based cladistic analysis was conducted on representatives of the freshwater crab families Deckeniidae, Gecarcinucidae, Parathelphusidae, Potamidae, Potamonautidae, Pseudothelphusidae, and Trichodactylidae using a disparate assemblage of marine heterotreme and thoracotreme brachyurans as possible sister groups. The monophyly of the freshwater crabs sensu lato is falsified. The family Trichodactylidae and the marine portunid subfamily Carcininae form basal groups within the superfamily Portunoidea. The monophyly of the Pseudothelphusidae and the Paleotropical freshwater crab families is supported, and this clade is the sister group of the Thoracotremata (Gecarcinidae, Grapsidae s.l., and Ocypodoidea). The origin, groundplan, and diversification of freshwater crabs are discussed in the context of previously published scenarios of their evolution.     

Phylogenetic analysis of the Brachyura (Crustacea, Decapoda) based on characters of the foregut with establishment of a new taxon

The Brachyura, within the decapod crustaceans, is one of the most species-rich taxa with up to 10 000 species. However, its phylogenetic history, evolution and fossil record remain subjects of controversy. In our study, we examined the phylogenetic relationships of the Brachyura based on morphological characters of the foregut. The cladistic analysis supports a monophyletic Brachyura including the Dromiidae and Raninidae. A clade comprising Dromiidae and Dynomenidae forms the most basal assemblage within the Brachyura, followed by the Homolidae and Latreilliidae. As a result, neither Podotremata nor Archaeobrachyura form a clade. In contrast, foregut data suggest that the classical taxon Oxystomata, comprising Calappidae, Parthenopidae, Dorippidae, Leucosiidae, Cymonomidae and Raninidae, is monophyletic. This makes the Heterotremata paraphyletic or polyphyletic. A newly established taxon, Neobrachyura, embraces some representatives of the Heterotremata and the monophyletic Thoracotremata.     

Molecular phylogeny and evolution of unique mud-using territorial behavior in ocypodid crabs (Crustacea: Brachyura: Ocypodidae)

Among crabs of the family Ocypodidae, Ilyoplax has been known to exhibit unique mud-using territorial behavior against neighbors, including neighbor burrow plugging, barricade building, and fence building. To assess the evolution of current behavioral forms observed in Ilyoplax, 1,416-bp nucleotide sequences from the mitochondrial 12S rRNA to 16S rRNA genes of 20 species, representing four recognized subfamilies of Ocypodidae, were analyzed. The resultant phylogenetic tree revealed the subfamily Dotillinae, including Ilyoplax, to be monophyletic, with a sister group relationship with subfamily Camptandriinae. These two subfamilies were branched after Ocypodinae, with Macrophthalminae being most basal. Species of Ilyoplax fell into three different Dotillinae lineages, indicating the genus to be polyphyletic. Crabs in two of the three lineages showed differential geographic distribution and body size. Phylogenetic analyses of behavioral characters demonstrated that mud-using techniques had evolved multiple times and sequentially. From their behavioral similarity and evolutionary occurrence, fence building is hypothesized to have evolved from barricade building, and the latter, from burrow plugging. This scenario also appeared reasonable with respect to behavioral trends observed in the field. The evolution of such territorial behavior is considered to be associated with ecological conditions such as burrow fidelity and substrate condition.      

Molecular phylogeny of grapsoid crabs (Decapoda, Brachyura) and allies based on two mitochondrial genes and a proposal for refraining from current superfamily classification

Grapsoid and ocypodoid crabs receive a lot of attention in the literature due to their predominance and important role as primary and secondary consumers in intertidal as well as supratidal marine habitats. They are especially species‐rich in the tropics, where they have been found to repeatedly invade terrestrial and freshwater habitats. However, the systematics of the crabs belonging to these two superfamilies is still not settled, despite recent steps clarifying phylogenetic relationships and introducing new taxa. In this study, a molecular phylogeny of grapsoid crabs primarily based on East African representatives is constructed based on DNA sequences of the mitochondrial small and large ribosomal subunits (12S and 16S rRNA), thus complementing previous molecular taxonomic studies that had been carried out with the American and East Asian fauna. In addition, selected representatives of all ocypodoid families and subfamilies were included. The monophyly of Grapsidae, Ocypodidae (sensu stuctu), Sesarmidae and Varunidae is well confirmed, if the genera Cyclograpsus, Helice are considered Varunidae and Euchirograpsus a Plagusiidae, as previously suggested. The monophyly of the family Gecarcinidae cannot be supported with our data. The family Plagusiidae in its present composition is polyphyletic. Special attention was given to the large family Sesarmidae, which has many endemic genera in the Indo‐West Pacific. According to this study, two of the most speciose genera, Chiromantes and Parasesarma, are not monophyletic and need to be redefined. On the higher taxonomic level, it becomes evident that both superfamilies, Grapsoidea and Ocypodoidea, are not monophyletic in their current composition, as exemplified by a proposed sister group relationship of Varunidae and Macrophthalmidae. These results confirm those from previous molecular studies and we therefore propose to refrain from the traditional use of the Grapsoidea and Ocypodoidea as monophyletic superfamilies and treat the constituent families separately.     

Not only for males: the pleon‐holding mechanism in female calappids (Crustacea: Decapoda: Brachyura)

Adult female Calappidae were examined with light microscopy and microcomputed tomography for the presence of a pleon‐holding mechanism. A typical press‐button consisting of a protrusion on the fifth thoracic sternite and a socket on the sixth pleon segment was found in species of the genera Calappa, Calappula, Cycloes, Mursia, and Paracyclois. Within the genus Calappa, 15 of 17 species showed a complete press‐button mechanism, whereas in two species only a sternal button or none of the holding structures could be observed. The functionality of the mechanism was assessed by manually flexing and opening the pleon. This revealed a lack of function in species with fully developed holding structures, while others exhibited full function. Additionally, signs of abrasive wear could be identified with scanning electron microscopy on the surface of the holding structures of Calappa hepatica. The documentation of pleon‐holding structures of varying degrees of functionality in adult female eubrachyurans provides new insight into a morphological characteristic known exclusively from Brachyura.     

The collision of the Indian plate with Asia: molecular evidence for its impact on the phylogeny of freshwater crabs (Brachyura: Potamidae)

Aim We used molecular data to answer the following questions: (1) Is morphology‐based (and to some extent, geography‐based) classification of the freshwater crab family Potamidae congruent with a molecular phylogeny? (2) What historical biogeographical event could have shaped this phylogeny? Location Material from the entire geographical range of the family Potamidae was analysed, including specimens from East Asia (China, Taiwan, the Ryukyus), Southeast Asia, South Asia (northern India, the Middle East and Near East), North Africa, and southern Europe. Methods Mitochondrial DNA sequences encoding 503 base pairs (excluding the variable regions) of the large subunit rRNA (16S rRNA) gene were obtained from 72 species belonging to 49 potamid genera, representing 51% of all known genera in this species‐rich family. Sequences were compared by means of phylogenetic analyses (minimum evolution, Bayesian inference, maximum likelihood and maximum parsimony) and Bayesian relaxed molecular clock estimates. Results The family Potamidae was found to be monophyletic with two major lineages, and there was support for the recognition of two mostly allopatric subfamilies, Potaminae and Potamiscinae. This is largely consistent with the current classification proposed. The ‘Potamiscinae’ clade comprised three subclades: (1) a well‐supported ‘eastern Asia’ subclade that included species from the eastern part of the range (China, Taiwan, the Ryukyus, the Philippines, Indochina, Malay Peninsula, northern India and Myanmar/Burma); (2) a weakly supported ‘Sunda Shelf islands’ subclade that included species from the larger Southeast Asian islands on the Sunda Shelf (Borneo, Sumatra and Java); and (3) a ‘Socotra’ subclade that comprised only Socotrapotamon from Socotra Island, off the north‐east coast of Africa. Main conclusions The discrete distribution of the two subfamilies in Europe/Asia is hypothesized to be the result of vicariance due to the collision of the Indian tectonic plate with the Asian continent, and the orogeny that caused the separation of the two freshwater crab lineages around 22.8 Ma. Within the Potamiscinae, the ‘Sunda Shelf islands’ subclade separated from other potamiscines around 21.1 Ma; and the endemic fauna of the East Asian islands (Taiwan, the Ryukyus and mainland Japan) was isolated from the Asian continent c. 8.4 Ma, following the opening of the Okinawa Trough. The ‘Socotra’ subclade diverged from the ‘eastern Asia’ subclade at 19.1 Ma during the Miocene. Its taxonomic position, however, remains unclear as the members of this clade possess the key potamine character of a transverse ridge on thoracic sternite 8, suggesting that this may in fact be a relict potamid group.     

Notes on the position of the true freshwater crabs within the brachyrhynchan Eubrachyura (Crustacea: Decapoda: Brachyura)

Cladistic and phenetic relationships of 51 eubrachyuran crab genera, comprising 36 genera of marine crabs and 18 genera of true freshwater crabs from 7 families, were investigated using 121 parsimony-informative adult morphological characters. The data matrix was subjected to four different treatments: (1) a cladistic analysis with a combination of unordered and ordered characters, (2) a cladistic analysis with all characters unordered, (3) neighbour-joining, and (4) UPGMA phenetic analyses. The parsimony analysis conducted with a combination of ordered and unordered characters produced a set of hypotheses which supported monophyly of a Pseudothelphusidae+Potamoidea clade. Furthermore, exemplar genera of the Bythograeidae and Pinnotheridae formed an unresolved polytomy with the Pseudothelphusidae+Potamoidea group, the Thoracotremata. The trichodactylid freshwater crabs were positioned as the sister taxon of the basal portunoid Carcinus, but were unresolved relative to other portunoids and geryonids. Second, the parsimony analysis conducted with all characters unordered resulted in a [bythograeid, pseudothelphusid+potamoid, pinnotherid, thoracotreme] group with no hierarchical resolution, which in turn formed a polytomy with a goneplacid+portunoid clade and a polyphyletic Xanthoidea. And third, phenetic groupings of the eubrachyuran genera invariably placed the pseudothelphusids with the potamoids, and this clustered with a group containing the thoracotremes (either in whole or part). Support was thus found for morphological connections among the nontrichodactylid freshwater crabs, thoracotremes, bythograeids, and pinnotherids, and for the placement of the trichodactylids within the Portunoidea. These two latter findings (that used a range of genera from each family) are broadly congruent with a previous cladistic analysis of selected eubrachyuran familial groundpatterns that used a basal exemplar of each marine and freshwater crab family (Sternberg et al., 1999). However, it is clear that the large scale homoplasy identified here may nullify any reliable hypothesis of brachyrhynchan groupings at this stage.     

Reproductive biology of the Suez Canal spider crab Schizophrys aspera (H. Milne Edwards, 1834: Crustacea: Brachyura: Majidae)

A reproductive biology study of the spider crab Schizophrys aspera (H. Milne Edwards, 1834) was conducted in the Suez Canal from July 2012 to June 2013. The annual sex ratio (Male:Female) of S. aspera was female biased with values of 1:1.25. Out of the four ovarian development stages of this crab, two stages were observed in the Suez Canal throughout the whole year. The ovigerous crab’s carapace width varied from 28 to 52 mm. This crab species can spawn during most of the year in the canal water, with a peak during late spring and early winter. The fecundity of ovigerous females ranged between 2349 and 13600 eggs with a mean of 5494 ± 1486 eggs. Female crabs that reached sexual maturity exhibited a minimum carapace width varying between 22 and 46 mm, and fifty percentage of all ovigerous females showed a carapace width of 36 mm.     

Morphology and function of the female reproductive system of Ebalia tumefacta (Decapoda,Brachyura, Leucosiidae)

In this article, the morphology and function of the female reproductive organs of Ebalia tumefacta were investigated using histological methods. While the vagina conforms to the concave type, the study reveals a new orientation of seminal receptacle compartments. The seminal receptacle consists of two chambers, which are oriented in anterior‐posterior direction. This is in contrast to the dorso‐ventral orientation of seminal receptacle chambers in all other known brachyuran crabs. The anterior chamber is lined by cuticle, whereas the posterior chamber is covered with a holocrine glandular epithelium. The oviduct connection is located ventrally, close to the opening of the vagina. The oviduct orifice is characterized by a transition of the epithelium lining of the oviduct to the seminal receptacle holocrine glandular epithelium. Special features are muscle fibers, which are attached to the oviduct orifice and to the sternal cuticle as well. The muscle fibers can be found exactly at that point where the oviduct opens into the seminal receptacle and are secondly attached to the sternum beneath. This musculature is newly described for Eubrachyuran crabs. This musculature can be interpreted as an important feature in the fertilization and egg‐laying process in relation to supporting and controling the inflow of eggs into the seminal receptacle lumen. These new discoveries were compared to the known pattern of an Eubrachyuran seminal receptacle. J. Morphol. 276:517–525, 2015. © 2014 Wiley Periodicals, Inc.     

Concluding contribution towards a revision of, and a key to, the genus Macrophthalmus (Crustacea: Brachyura)

In this ninth and final part of a revision of the ocypodid genus Macrophthalmus Latreille (Crustacea: Brachyura), eight species are considered— M. leptophthalmus (H. M. Edw.), M. boteltobagoe (Sakai), M. philippinensis SereGne, M. consobrinus Nobili, M. gastrodes Kemp, M. franchettii Maccagno, M. gallardoi SereGne and M. vietnamensis SereGne—and the status of a species previously considered valid, M. holthuisi SereGne, is reconsidered. Only M. leptophthalmus, M. boteltobagoe and M. philippinensis are considered valid. Macrophthalmus , as here revised, contains 38 living and three extinct species, whilst 33 species have been reduced to synonyms. These various species are summarily listed and a key to the living species is provided.     

Molecular phylogeny of the western Atlantic species of the genus Portunus (Crustacea, Brachyura, Portunidae)

The genus Portunus encompasses a comparatively large number of species distributed worldwide in temperate to tropical waters. Although much has been reported about the biology of selected species, taxonomic identification of several species is problematic on the basis of strictly adult morphology. Relationships among species of the genus are also poorly understood, and systematic review of the group is long overdue. Prior to the present study, there had been no comprehensive attempt to resolve taxonomic questions or determine evolutionary relationships within this genus on the basis of molecular genetics. Phylogenetic relationships among 14 putative species of Portunus from the Gulf of Mexico and other waters of the western Atlantic were examined using 16S sequences of the rRNA gene. The resultant molecularly based phylogeny disagrees in several respects with current morphologically based classification of Portunus from this geographical region. Of the 14 species generally recognized, only 12 appear to be valid. We recommend that P. vossi be hereafter regarded as a junior synonym of P. spinimanus and that P. bahamensis be regarded as a junior synonym of P. depressifrons . Our analysis suggests that western Atlantic members of the genus can be subdivided into at least three well-defined clades. Pending further molecular analyses with a large subset of species, it appears that the genus is not monophyletic and that it warrants further taxonomic revision.  © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society , 2007, 150 , 211–220.     

Comparative study of the morphology of the female seminal receptacles of Ilia nucleus and Persephona mediterranea (Decapoda,Brachyura, Leucosiidae)

Because of the poor knowledge of the morphology of the female reproductive organs of most brachyuran crabs, this study investigated two Atlantic representatives of the family Leucosiidae, Ilia nucleus (Linnaeus, 1758) and Persephona mediterranea (Herbst, 1794), using histological methods and magnetic resonance imaging (MRI). While the vagina conforms to the concave type, the arrangement of the two chambers of the seminal receptacle differs strongly from that of other eubrachyuran sperm storage organs. Both chambers are oriented laterally within the crab's body. This is in contrast to the dorso-ventral orientation described in most other known brachyuran crabs. The lateral chamber is covered by cuticle, whereas the medial chamber is covered by a holocrine glandular epithelium. The oviduct connection is located ventrally, posterior to the vagina. The oviduct orifice is characterized by a transition from the epithelium lining the oviduct to the seminal receptacle's holocrine glandular epithelium. Moreover, muscle fibres are attached to the oviduct orifice and to the sternal cuticle. This musculature can be interpreted as an important feature in the fertilization and egg-laying process by supporting and controlling the inflow of eggs into the seminal receptacle lumen. The results of this study are compared to the morphology of the seminal receptacle of another leucosiid crab, Ebalia tumefacta (Montagu, 1808), and to those of other known eubrachyuran crabs.     

Two species of swimming crabs of the genus Achelous (Crustacea,Brachyura): environmental requirements determining the niche

Some holoplanktonic species are cosmopolitan and have continuous distribution in the world’s oceans. For most of these species it is not clear whether there is unhampered gene flow between far distant populations or they represent a complex of cryptic species. In the present study we investigated genetic diversity of the cosmopolitan chaetognath Eukrohnia hamata in order to identify its spatial structure. DNA-barcode fragment of the mitochondrial COI gene was determined and analyzed for E. hamata specimens collected in the Arctic Ocean, Atlantic Ocean, and Atlantic sector of the Southern Ocean. Five lineages were determined by the phylogenetic analysis with robust statistical support. Three lineages: Antarctic (Eh-1), Subantarctic (Eh-2), and Arctic (Eh-3) had significant genetic differences and were geographically separated. Two other lineages: Eh-4 and Eh-5, that had the smallest genetic difference, were observed together in tropical waters, but they were geographically separated from the other lineages. We suppose that geographical distribution of most of the E. hamata lineages is shaped by the large-scale oceanic fronts, considered as biogeographic boundaries for numerous zooplankton species. Genetic homogeneity of Arctic, Subantarctic, and Antarctic lineages was also shown, each within its regions of inhabit.     

Phylogenetic relationships, character evolution, and taxonomic implications within the slipper lobsters (Crustacea: Decapoda: Scyllaridae)

The slipper lobsters belong to the family Scyllaridae which contains a total of 20 genera and 89 species distributed across four subfamilies (Arctidinae, Ibacinae, Scyllarinae, and Theninae). We have collected nucleotide sequence data from regions of five different genes (16S, 18S, COI, 28S, H3) to estimate phylogenetic relationships among 54 species from the Scyllaridae with a focus on the species rich subfamily Scyllarinae. We have included in our analyses at least one representative from all 20 genera in the Scyllaridae and 35 of the 52 species within the Scyllarinae. Our resulting phylogenetic estimate shows the subfamilies are monophyletic, except for Ibacinae, which has paraphyletic relationships among genera. Many of the genera within the Scyllarinae form non-monophyletic groups, while the genera from all other subfamilies form well supported clades. We discuss the implications of this history on the evolution of morphological characters and ecological transitions (nearshore vs. offshore) within the slipper lobsters. Finally, we identify, through ancestral state character reconstructions, key morphological features diagnostic of the major clades of diversity within the Scyllaridae and relate this character evolution to current taxonomy and classification.     

Phylogeny, biogeography and a new taxonomy for the Gecarcinucoidea Rathbun, 1904 (Decapoda: Brachyura)

Phylogenetic relationships of gecarcinucoid freshwater crabs were investigated, based on morphology of the male second gonopod. In addition, a comparison of sequences from the mitochondrial large subunit rRNA gene helped to resolve the phylogeny of this group and relationships to other Old World freshwater crabs. As a result, we recognise two sister groups within the Gecarcinucoidea, the African Deckeniidae and the Asian Gecarcinucidae. Deckeniidae includes three monophyletic clades, the Deckeniinae in East Africa and on the Seychelles, the West African Globonautinae and the Malagasy Hydrothelphusinae. Gecarcinucidae comprises two sister groups, the Gecarcinucinae with representatives in Sri Lanka, India and southeast Asia, and the Parathelphusinae in India, southeast Asia, the Sundaic Islands and Australia. Interpretation of our phylogenetic results leads us to propose a new biogeographic hypothesis for the Gecarcinucoidea. Most likely, the gecarcinucoid freshwater crabs have an African origin; their distribution can be explained by successive events of dispersal. This model can be correlated with palaeogeographical and palaeoclimatological data for the Cenozoic, suggesting a gecarcinucoid dispersal to Asia via the “Lemurian Stepping-Stones”, a chain of islands in the West-Indian Ocean that were emergent in times of low sea levels during the Oligocene.     

A molecular phylogeny of Bopyroidea and Cryptoniscoidea (Crustacea: Isopoda)

Epicaridean isopods are parasitic on other crustaceans. They represent a diverse group of highly derived taxa in two superfamilies and 10 families. Little work has been done on the phylogeny of these parasites because of the difficulty in defining homologous characters for adults above the genus level. The females exhibit morphological reduction of characters and the males have few distinguishing characters. Moreover, epicarideans have only rarely been included in past studies of isopod phylogeny. Our objective was to derive a phylogeny of epicaridean taxa based on 18S rDNA, then use that phylogeny to examine the relationships of the bopyrid subfamilies, bopyroid families and epicarideans to cymothoid isopods. We tested the monophyly of the Epicaridea, evaluated hypotheses on relationships among epicaridean families and subfamilies, examined the evolution of the abdominal mode of infestation on caridean, gebiidean, axiidean and anomuran hosts and examined coevolution between epicarideans and their crustacean hosts. The molecular phylogeny indicated that Epicaridea were monophyletic with respect to Cymothooidea. Bopyroidea formed a monophyletic group without Dajidae and Entophilinae (now as Entophilidae). Both latter taxa grouped with Cryptoniscoidea, and this group was the sister taxon to the redefined Bopyroidea in all trees. The bopyrid subfamily Ioninae is the sister taxon to the other bopyrid subfamilies (except Entophilidae). Ioninae was elevated to family status but found not to be monophyletic; a new subfamily, Keponinae, was erected for all genera formerly placed in Ioninae except the type genus. The abdominal mode of parasitism appears to have evolved independently among the subfamilies. Coevolution between host and parasite phylogenies showed extensive incongruence, indicating frequent host-switching as a general pattern in Epicaridea.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:30ECFB13-2795-494E-AABE-6B5F84A57A67     

Comparative spermatozoal ultrastructure and molecular analysis in dromiid crabs and their phylogenetic implications for Dromiidae and Podotremata (Decapoda: Brachyura)

We described the spermatozoal ultrastructure and conducted a molecular analysis of Dromiidae Hypoconcha parasitica, Hypoconcha arcuata, Moreiradromia antillensis and Dromia erythropus. To elucidate the relationship between the different species of this brachyuran group, we also compared the spermatozoal morphologies and phylogenetic positioning among species of Dromiidae, Dromioidea and Podotremata. Specimens were collected from the northern coast of São Paulo, Brazil and were fixed and processed followed by transmission electron microscopy and molecular analysis routines. The Dromiidae spermatozoa studied are characterized by a discoidal acrosome, with three or four concentric zones, which are centrally separated by a bilaterally capitate perforatorial chamber, with a “mushroom”-shaped apex in the Hypoconchinae and a “T-shape” in Dromiinae. Above the perforatorial chamber, there is an apical protuberance, continuous with the subopercular region and the operculum, which forms a low, centrally perforated dome. Under differential interference contrast microscopy, the spermatozoa show 3 to 4 radial arms. The spermatozoal characters in Hypoconchinae and Dromiinae do not separate these subfamilies from the Dromiidae and Dromioidea. Ultrastructural differentiation was only found between representative Dromioidea and other Podotremata. Thus, the spermiotaxonomy of these Hypoconcha, Moreiradromia and Dromia species corroborated previous morphological and molecular studies, supporting the monophyly of Dromiidae and Dynomenidae in relation to Homolidae and Latreilliidae.