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We report on the freshwater crabs of the families Potamidae, Gecarcinucidae, and Sesarmidae in the archipelago of Anambas and Natuna Islands in Indonesia. Five genera (one new) and eight species (four new) are now recorded from the islands. For the Potamidae, a new genus and a new species, Natunamon indonesicumn. sp., is described from Natuna; the taxon has diagnostic characters intermediate between IsolapotamonBott, 1968 and IbanumNg, 1995 from Borneo. A new species of Isolapotamon, I. remotumn. sp., is also described from Anambas; this is the first record of the genus outside Borneo and Mindanao, Philippines. For the Gecarcinucidae, the rare Balssiathelphusa natunaensisBott, 1970 is collected for the first time since its description, although the type was collected over 120 years ago; the species is redescribed in detail and the composition of the genus discussed. The widely distributed gecarcinucid, Parathelphusa maculataDe Man, 1879 is also recorded from Anambas and Natuna. Four species of Sesarmidae are reported: Geosesarma insulare Ng, 1986 (from Anambas), G. teschi Ng, 1986 (from Natuna), G. anambasn. sp. (from Anambas) and G. hashimin. sp. (from Natuna). Geosesarma hashimin. sp. is an arboreal species with a suite of atypical characters that suggest its present classification in Geosesarma needs to be reassessed.

The pilumnid crab Pilumnopeus convexus (Maccagno, 1936), native to the Arabian Sea and western Indian Ocean, has been discovered among intertidal fouling communities along shores of Hong Kong. The species was first discovered in 2011 and is believed to have become established by around 2016. Material from local sites was compared with specimens from Iran and Pakistan, and the identification was supported by molecular analyses using mtDNA COI gene sequences. This species is not yet known from East and Southeast Asia, and was probably transported to Hong Kong by international maritime shipping, likely in the ballast water or on the hulls of ships, and subsequently survived as a non-indigenous species (NIS). This represents the first case of west-to-east invasion of brachyuran crabs from the Indian Ocean reaching sub-tropical East Asia. Past studies on the local intertidal fauna, and documentations of NIS, are briefly discussed.

The Australian southern giant crab, Pseudocarcinus gigas (Lamarck, 1818), has traditionally been placed in the families Oziidae Dana, 1851 or Menippidae Ortmann, 1893 (superfamily Eriphioidea MacLeay, 1838). Previous genetic studies questioned the validity of this classification as the molecular markers placed it far from all eriphioid lineages. A morphological re-examination of P. gigas shows that it possesses a suite of unusual characters in the structure of the antennae, antennules, epistome, carapace, pereopods, thoracic sternum, and vulvae that show it is different from other Eriphioidea as well as all other extant heterotremes, confirming the genetic results. A new family, Pseudocarcinidae, and a new superfamily, Pseudocarcinoidea, both monotypic, are here established for P. gigas.

Telphusa austeniana Wood-Mason, 1871 is a poorly known potamid crab described from a single female specimen from Meghalaya state, northeastern India, and its position in Tiwaripotamon Bott, 1970 has been questioned. Its systematic position is now clarified based on the examination of the female holotype and a male specimen recently collected from a cave near the type locality. The species is transferred from Tiwaripotamon to a new genus, Krishnamongen. nov. on the basis of the differences in the structures of the epigastric cristae, male pleon, male sixth pleonal somite, male telson, gonopods, and vulvae. The geographic distributions of the two genera are some 1,000 km apart. The new genus has affinities with Doimon Yeo & Ng, 2007, and Indochinamon Yeo & Ng, 2007, but can be distinguished mainly by its extremely slender and elongated ambulatory legs. While Krishnamon austenianum (Wood-Mason, 1871) comb. nov. is now recorded from limestone caves, it does not, however, possess the troglomorphic features of an obligate troglobite.

The Japanese spider crab, Macrocheira kaempferi (Temminck, 1836), the largest living arthropod in the world, was originally placed in the family Majidae Samouelle, 1819 as a monotypic subfamily, Macrocheirinae Dana, 1851. While various authors have treated the taxon as belonging to its own superfamily, family, subfamily, or even tribe, the consensus of modern taxonomic system has for the most part considered it to be simply a genus within Inachidae MacLeay, 1838 (superfamily Majoidea Samouelle, 1819). Strangely, however, considering its size and fame, its adult morphology has remained poorly studied. Recent larval and genetic studies have raised questions regarding its suprageneric status, suggesting an independent evolutionary position within Majoidea and the recognition of a separate family. We examined and compared a large suite of adult characters in Macrocheira De Haan, 1839 against other potentially related majoid groups, and found unique characters that support the larval evidence for monophyly of the genus. It is thus necessary to re-establish a monotypic Macrocheiridae for Macrocheira. A molecular phylogeny reconstructed from mitochondrial 16S rRNA gene is presented in further support of this conclusion, showing Macrocheira as sister to Oregoniidae Garth, 1958 and distant from Inachidae. A new diagnosis for the family is provided. Macrocheiridae differs from the morphologically most similar families, Inachidae and Oregoniidae, by characters associated with the carapace, thoracic sternum, male pleon, gonopod, and vulvae.

Xanthid crabs of the genus TweedieiaWard, 1935, are among the most beautiful decapod cryptofauna in Indo-West Pacific coral reefs, with an ornate arrangement of granules and setae, in combination with an eye-catching color pattern. The genus and three recognised species (T. odhneri (Gordon, 1934), T. laysani (Rathbun, 1906), and T. brevidactylaDai & Yang, 1998) are revised, and new diagnoses and figures are provided. The COI barcoding gene of 38 specimens was sequenced and used to generate maximum likelihood and neighbor-joining trees. Tweeedieia brevidactyla is here synonymized with T. odhneri. Tweedieia now comprises only two species, differentiated by morphological characters and sequence data. Tweedieia odhneri ranges from the western Indian Ocean to the Hawaiian Islands and French Polynesia, while the rare T. laysani is only recorded from the Hawaiian Islands. These crabs appear to favor clear, oligotrophic, oceanic waters and are common on oceanic islands and rare around continents and large islands of Australasia.

A new genus and new species of xanthid crab, Mabui calculusn. gen., n. sp., are described from Okinawa Island, Ryukyu Islands, Japan. The new taxon is unique for Brachyura by having bilaterally asymmetrical male gonopods and female gonopores, with the particular reproductive structure always distinctly more developed on one side than in the other. This remarkable condition, so far unique among brachyurans, was observed in all specimens examined (N = 53), except for an undeveloped subadult female. The right chelae of all intact males and large females are almost always larger than the left chela, and each right chela has a large and modified cutting tooth. Other than in the asymmetrical external reproductive structures, the new taxon is morphologically closest to the xanthines Megametope ogaensis Sakai, 1974 and Jacforus cavatus (Rathbun, 1907), but can easily be distinguished by the characters of the carapace, third maxilliped, ambulatory legs, and male pleon.

The taxonomy of the pilumnoid genus ParapanopeDe Man, 1895 is revisited and two new species are recognised. With a better series of specimens, more differences between the type species, P. euagoraDe Man, 1895 (from Java), and the morphologically similar P. hextii (Alcock, 1898) (from India) are documented. Specimens previously identified as P. euagora from China, Japan, and Korea are here referred to a new species, P. orientalisn. sp.; while others from Malaysia previously assigned to P. cultripes (Alcock, 1898) are here regarded as P. parvan. sp.Parapanope hextii is recorded from Malaysia, Singapore, and Brunei for the first time, while P. siamensis is a new record for China. The identity of the poorly known P. pagenstecheri (Neumann, 1878) from India and its possible conspecificity with P. hextii also discussed. A key to the eight species of Parapanope now recognised is also presented.

The poorly known sesarmid crab Sesarma (Holometopus) tangi Rathbun, 1931 was described from one male from Fujian, China, and was transferred to Neosarmatium Serène & Soh, 1970 by Schubart & Ng (2002). The collection of a good series of fresh specimens from near the type locality and Hong Kong allows us to reappraise its taxonomy. The new material shows that Sesarma tangi should be referred to its own genus, differing markedly from congeners in the detailed structure of its male and female chelae as well as in the form of the male first gonopods. This conclusion is strongly supported by genetic data.

Potamid freshwater crabs are characterised by mandibular palps possessing three segments with the terminal lobe simple. A new genus and new species of semi-terrestrial crab, Gempala bilobata , is here described from Peninsular Malaysia that possesses a 3-segmented mandibular palp having a bilobed terminal segment, a hitherto unknown condition. In addition, the carapace of the new genus is unusually high. Comparisons with allied potamid genera from Malaysia are also made and the affinities of the genus discussed.

The western Pacific pinnotherid crab, Fabia obtusidentata Dai, Feng, Song and Chen, 1980, which lives in the saucer scallop, Amusium (Pectinidae), is found not to belong to Fabia Dana, 1851 s. str. or Pinnotheres Bosc, 1802. In contrast to these two genera, F. obtusidentata possesses a carapace not having longitudinal grooves, a third maxilliped in which the dactylus is slender and inserted one-third from the proximal end of the conical propodus, and a prominently elongated right third ambulatory leg with a long dactylus. It is here referred to its own genus, Amusiotheres gen. nov. Pinnotheres hanumantharaoi Devi and Shyamasundari, 1989, from India, is also transferred to the new genus.

The mathildellid crab genus Neopilumnoplax Serene in Guinot, 1969 was originally proposed for several deep-sea species previously placed in Pilumnoplax Stimpson, 1858, including P. sinclairi Alcock and Anderson, 1899 from the Bay of Bengal. Further revision led to creation of Mathildella Guinot and Richer de Forges, 1981, which differed chiefly from Neopilumnoplax in having one instead of two pairs of endostomial ridges, and in the width of the anterior abdominal somites. Most species of both genera are relatively well known, but N. sinclairi , until now, was known with certainty only from the type description and figure of the female holotype housed in the collections of the Zoological Survey of India. Examination of the holotype of Pilumnoplax sinclairi , facilitated by the late Michael Turkay, revealed P. sinclairi to belong to Mathildella instead of Neopilumnoplax . Moreover, comparison of M. sinclairi with M. kyushupalauensis Takeda and Watabe, 2004 from Komahashi Seamount off Japan revealed that the two nominal species may well be synonyms. We defer synonymising the two species, however, until male M. sinclairi can be studied. We also clarify selected historical records of “ Pilumnoplax ” species from Indonesia and mainland Japan, from which we confirm the occurrence of Mathildella serrata (Sakai, 1974) and M. kyushupalauensis , respectively. In addition, we recognise an additional character separating Neopilumnoplax from Mathildella in the respective presence or absence of epibranchial ridges on the carapace. Neopilumnoplax michalis sp. nov. from the Southwest Indian Ocean Ridge is described and compared with its nearest congener, N. heterochir (Studer, 1883) from off southern Africa. The identity of Pseudorhombilia ( Pilumnoplax ) normani Miers in Tizzard, Moseley, Buchanan and Murray, 1885 from Nightingale Island (Tristan da Cunha) and Agulhas Bank, off South Africa, is fixed by lectotype designation as a junior synonym of N. heterochir .

Cancer is one of the “oldest” names in carcinology, but like many old and familiar things it has fallen into use as a catch-all category, especially by non-taxonomists. Much taxonomic revision has occurred in Brachyura: Cancridae [Cancer] in recent years, and unfortunately, much of it has passed completely under the radar of biologists. A summary of that revisionary work is provided along with a list of currently accepted names for the living species of Cancridae. We offer this contribution in an effort to cut off the use of old, and in many cases invalid, binomina, and to encourage the use of a modern, up-to-date classification of cancrid crabs.

The taxonomy of the rare Macrophthalmus leptophthalmus (H. Milne Edwards, 1852) is reviewed. On the basis of distinctive features of the carapace, eyes, and epistome, M. leptophthalmus is assigned to the subgenus, Euplax H. Milne Edwards, 1852, new status, a taxon that has been incorrectly synonymised under Macrophthalmus (Venitus) Barnes, 1967. A related species, Macrophthalmus (Euplax) dagohoyi, new species, is described from subtidal mangroves in Bohol, central Philippines. Macrophthalmus (Euplax) dagohoyi can easily be distinguished from M. (Euplax) leptophthalmus by different carapace, cheliped, walking leg and sternal characters. A key to the genera and subgenera of Macrophthalmidae is also presented.

The taxonomic status of the six Japanese species of Caridina described by W. Stimpson (1860) is clarified on the basis of fresh specimens from the type localities. Caridina grandirostris, which has long been synonymized under C. longirostris H. Milne Edwards, 1837, is shown to be a distinct species; C. leucosticta is redescribed; C. multidentata is the senior synonym of C. japonica De Man, 1892; C. acuminata and C. brevirostris are regarded as junior synonyms of Atyoida pilipes (Newport, 1847); and C. exilirostris is synonymized with C. typus H. Milne Edwards, 1837. Neotypes for the six species are designated to stabilize their taxonomy, all of which are redescribed and figured. The various nomenclatural problems associated with these species are discussed.

The systematics of the Calappa lophos species group is clarified using morphological and molecular data. The phylogeny of some Indo-Pacific species of Calappa is discussed. Two species, C. quadrimaculata Takeda and Shikatani, 1990, and C. guerini (Brito-Capello, 1871), previously synonymised with C. lophos (Herbst, 1782), are shown to be valid species using morphological and molecular data. A new species in the group, C. acutispina, is described from Madagascar. The usefulness of Bayesian inference in elucidating the phylogenetic relationships of some of the species of Calappa based on partial cytochrome oxidase I (COI) sequences is examined.

Morphological heterogeneity of the pinnotherid genera Durckheimia and Xanthasia has long been recognised. In particular, the segmentation of the third maxilliped palp, whether 2- or 3-segmented, is presently regarded as a conservative and useful generic trait. Durckheimia and Xanthasia, however, both contain species with both types of third maxilliped palps. Prior to the present study, five species were placed in Durckheimia, four bearing a 3-segmented palp and one, D. besutensis, with a 2-segmented palp. Durckheimia is restricted to three species, D. carinipes (type species), D. caeca, and D. lochi. Durckheimia yokotai is synonymised with D. caeca. The aberrant D. besutensis is transferred to a new genus, Serenotheres. Xanthasia is restricted to its type species, X. murigera, which bears a 2-segmented palp. Xanthasia whitei, with a 3-segmented third maxilliped palp and only superficially resembling X. murigera, is made the type of a new genus, Tridacnotheres. All species are illustrated and diag...

The first stage zoea and megalopa of the hydrothermal vent crab Xenograpsus testudinatus Ng, Huang, and Ho, 2000, are described, figured, and compared with a typical varunid, Brachynotus sexdentatus (Risso, 1827). Further comparisons are made between the first stage zoea of X. testudinatus and those representing the remaining current families of the Grapsoidea, namely Gecarcinidae, Glytograpsidae, Grapsidae, Plagusiidae, and Sesarmidae. A number of zoeal characters, including (1) the absence of the antennal exopod, (2) the setal formula [0,4] for the maxillular endopod, (3) the presence of a spine on both the distal coxal and proximal basal lobes of the maxilla, and (4) the presence of a minute spine on the lateral margin of the telson fork, appear to distinguish X. testudinatus first stage zoea from all the other grapsoids examined for this study. The zoeal evidence suggests that Xenograpsus is significantly different from known grapsoid larvae and the genus should eventually be removed from the...

Two new species and two new records of the family Camptandriidae are reported from mangroves in the southwest coast of Irian Jaya, Indonesia. Paracleistostoma laciniatum, new species, and P. quadratum, new species, differ from congeners in the form of the male first pleopod, which is long and cylindrical in the first species, and short and rounded in the second. Paracleistostoma mcneilli (Ward, 1933) and Baruna trigranulum (Dai and Song, 1986) are recorded for the first time from Indonesian waters.

Hexapodid crabs are recorded from Taiwan for the first time. A new genus and new species, Latohexapus granosus, is described. Most similar to Hexapus and Hexapinus, Latohexapus can easily be distinguished by its proportionately much broader carapace with prominent granulated and well-defined regions, a very broad thoracic sternum which has a deep transverse groove between thoracic sternites 3 and 4, and a male first pleopod which extends well beyond the male telson. Paeduma orientalis (Rathbun, 1909) is also recorded from Taiwan on the basis of a female specimen.

The first zoea of Lauridromia indica (Gray, 1831) is described and compared with other dromiid larvae. Forty-six characters of dromiid first zoea and megalopa larvae (seven genera and 11 species) are summarized, and their concordance with the taxonomy of recently revised genera, based on adult morphology, is tested. For the most part, larval characters support the new generic arrangement of McLay (1993). However, the larvae of Dromia wilsoni are very different from those of congeners, suggesting that it should be placed in a new genus. Almost half of the species whose larvae are known show various degrees of abbreviated development. All known dromiids with direct development occur in Australian waters. This mode of development is not confined to a monophyletic group of dromiids and seems to have evolved independently several times. The distinctiveness of the shell-carrying genera Conchoecetes and Hypoconcha is reinforced by larval characters and their similarity suggests descent from a common anc...

Twenty-six species of freshwater shrimps and crabs, belonging to 14 genera of four families (Atyidae, Palaemonidae, Parathelphusidae, and Grapsidae) are reported from Halmahera, Indonesia. Of them, 10 are new records for the island while one species of Macrobrachium is here described as new. Description for new species, diagnoses for poorly known species, and taxonomic discussions for all species are provided.

The freshwater crabs of the genus Tiwaripotamon Bott, 1970 (Potamidae) are revised and the identities of two poorly known species, T. simulum (Alcock, 1909) and T. araneum (Rathbun, 1905), are clarified after a re-examination of the types. Tiwaripotamon, sensu stricto, is restricted to five species, T. annamense (Balss, 1914); T. araneum (Rathbun, 1905); T. pingguoense Dai and Naiyanetr, 1994; T. xiurenense Dai and Naiyanetr, 1994; and a new species, T. edostilus, from Vietnam. Tiwaripotamon simulum is transferred to the genus Kanpotamon Ng and Naiyanetr, 1993. Keys to the species of Tiwaripotamon and Kanpotamon are also provided.

The taxonomy of the deep-water portunid genus Benthochascon Alcock and Anderson, 1899, is reappraised. Benthochascon is now restricted for its type species from the Indo-West Pacific, Benthochascon hemingi Alcock and Anderson, 1899. Benthochascon schmitti Rathbun, 1931, from the Gulf of Mexico, is referred to a new genus, Raymanninus, which differs from Benthochascon s. str. in the the form of the anterolateral margin, first and third maxillipeds, chela, and structure of the fourth male thoracic stemite.

The taxonomy of the Indochinese potamid waterfall crabs of the genus Demanietta from Thailand and Myanmar (=Burma) is revised, and the type species D. manii is redescribed. The genus now contains 10 species, 5 of which are new, namely, D. huahin, D. khirikhan, D. lansak, D. nakhonsi, and D. suanphung. A key to the species of Demanietta is provided.

The complete larval development of the brachyuran crab Zebrida adamsii White, an obligate symbiont of sea urchins, is described and illustrated. This species has 4 zoeal and 1 megalopal stages. The larval features indicate that the family Eumedonidae should be treated as a separate family within the superfamily Xanthoidea.

The taxonomy of Echinoecus, a genus of crabs symbiotic with sea urchins, is revised. The genus Proechinoecu.s is a synonym of Echinoecus. Echinoecus, as here defined, contains 3 species: E. pentagonus, E. nipponicus, and E sculptus.

A new genus and species of troglobitic potamid crab is described from central Laos. The new taxon possesses a unique combination of morphological characters not found in any other known fresh-water crabs. Key diagnostic characters include the compressed frontal regions, reduced eyes, auriculiform merus of the third maxilliped, long ambulatory legs, and unusual male first pleopod structure. The reduced eyes and extremely long slender legs make this species the most highly modified cave-dwelling crab reported thus far from Indochina.

The varunine crab genus Neoeriocheir, previously synonymized under Eriocheir, is here regarded as a valid taxon. The type species, N. leptognathus, differs from members of Eriocheir sensu stricto in the form of its epistome, chelipeds, and male first pleopod as well as first zoeal structures. Eriocheirformosa is here assigned to a new genus, Platyeriocheir. The type species, Eriocheir formosa, is distinctly different from species of Eriocheir sensu stricto based on the structure of the carapace, the chelipeds, the thoracic sternum, and the male first pleopod, and on the form of the zoeal and megalopal stages.

The taxonomy of Thelphusula, a Bornean genus of gecarcinucid fresh-water crabs is revised. Two new species, T. sabana and T. tawauensis, both from Sabah, are described. A new genus and new species, Coccusa isophallus, which closely resembles Thelphusula, is described from Kalimantan. The affinities of Terrathelphusa adipis are reassessed and the species is transferred to Coccusa.

The complete larval development of Cryptodromia pileifera Alcock, 1899, under laboratory conditions, is described. It consists of only one zoeal and one megalopal stage. This is the first dromiid crab reported to have only one zoeal stage. The zoea is unique in that it lacks the hairlike process on the telson that is characteristic of all other known dromiid larvae. The presence or absence of free-swimming larval stages in the life cycles and their effect on the distribution of the Dromiidae are also briefly discussed.