Mani Prema

Three new brachyuran crab species of Hexapodidae are described from the Arabian Sea and Bay of Bengal, based on material collected by FORV Sagar Sampada between 2015 and 2019, with the genera Mariaplax Rahayu & Ng, 2014, and Hexapinus Manning & Holthuis, 1981, reported from Indian waters for the first time. Mariaplax kochazhi sp. nov ., and M. albucus sp. nov . were collected from the Arabian Sea at a depth 30 m while Hexapinus clivus sp. nov . was collected from the Bay of Bengal. Mariaplax kochazhi sp. nov . is most similar to M. granulifera (Campbell & Stephensen, 1970) from Australia but can be distinguished by its proportionately wider carapace with the surfaces possessing larger granules, the pterygostomial region smooth with 5–7 striae, a rectangular ischium and more granulated merus of the third maxilliped, a subpentagonal male pleon telson, and a strongly curved S-shaped male first gonopod with a rounded distal tip. Mariaplax albucus sp. nov . is similar to M. sundaica Rahayu & Widyastuti, 2018, from Java, but can easily be differentiated by a carapace that is as long as wide, a pterygostomial region that has 6 oblique striae, a relatively shorter and stouter P4 merus (4.0 times wider than long) and the distinctive structure of the vulva. In the latter species, the vulval operculum cover differs markedly from M. kochazhi , which is simple, rounded, and lacks a cover. Hexapinus clivus sp. nov . is morphologically close to the widely distributed H. simplex Rahayu & Ng, 2014, from the West Pacific, but it can easily be differentiated by the weaker granulation on the carapace surface; possession of a relatively shorter and stouter P4 merus (2.5 times as long as wide); a proportionately wider male thoracic sternum, with the fused sternites 1 and 2 being subtriangular and the lateral margins gently sloping; and the semilunate vulva elevated and protruded, and positioned adjacent to the suture between sternites 5 and 6.

A new species of dotillid crab, Ilyoplax kagga sp. nov ., is described from the Aghanashini River Estuary, a RAMSAR site on the west coast of India. It differs from its closest congener I. gangetica (Kemp, 1919) by marked differences in carapace features (shape, anterolateral armature, structure of the stridulatory ridges, and the number and kind of tubercles present), dentition on the carpus and palm of the chela, extent of setae on the ambulatory legs, as well as the structure of the male first gonopods.

The deep-water euryplacid crab, Nectopanope rhodobaphes Wood-Mason in Wood-Mason & Alcock, 1891, is monotypic and was originally described from one female from the Bay of Bengal, 18°30′N 84°46′E, a location off the coast of Andhra Pradesh in India. This species has only been reported subsequently by Ng et al. (2019) from a first male specimen collected in southern India. Recent collections of N. rhodobaphes from off Tamil Nadu in India obtained good series of male and female specimens. The study of these specimens revealed a degree of size-associated variations in the structures of the anterolateral teeth, as well as branchial regions of the carapace and first male gonopods. Scanning Electron Microscopy was used to record the microstructures associated with the female sternum, gonopods and vulva. Also, recorded is its live colouration. The swollen branchial regions of this species are not due to parasitism but shown to be natural and could indicate it may occur in oxygen poor areas of the deep-sea.

The goneplacid crab, Carcinoplax mistio Ng & Mitra, 2019, was originally described from West Bengal, India, in the northern Indian Ocean. Additional material of C. mistio from off Tamil Nadu in the southeast of India revealed a high degree of size-associated variation in the structures of the anterolateral tooth of the carapace, chelipeds, and male and female pleons. In addition to an in-depth morphological examination of C. mistio, this study also records the natural coloration of the species and conducts a genetic comparison (with mitochondrial COI and 16S rRNA genes) with its close relatives, C. haswelli (Miers, 1884) and C. purpurea Rathbun, 1914. Molecular comparison of C. mistio with its morphologically closest congener, C. haswelli from northern Australia and the western Pacific, corroborates their status as separate species. The genetic sequence of C. mistio, however, is similar to that of C. purpurea from the West Pacific, although these two species can easily be distinguished by distinct carapace and ambulatory leg characters. The present study provides some possible explanations for the genetic and morphological incongruence observed between C. mistio and C. purpurea and highlights the need for a detailed molecular study for Carcinoplax H. Milne Edwards, 1852, to appreciate the evolution of various morphological characters in the genus.

A new dromiid crab, Epigodromia mclayi sp. nov., is described from the southeastern Arabian Sea and southwestern Bay of Bengal, India, based on 2 males collected onboard FORV Sagar Sampada cruises 392 and 236, respectively at depths of 107–113 m. Epigodromia mclayi sp. nov., resembles E. areolata (Ihle, 1913) from Indonesia and Australia but can be easily distinguished by the conspicuously rounded carapace with well-defined regions and areolate ornamentation, anterolateral margin with two lobes, each adorned with small 5–9 distinct teeth, relatively more inflated branchial region, presence of a large conical tooth behind the posterior branchial granular node, large rounded granular chelipeds, not strongly dimorphic, more tubular ambulatory legs with nodules on meri and propodi, dactyli with 5–7 small spines, and strongly reduced last pair of legs with propodi bearing three similar sized spines on the anterior margin and a distal spine on the posterior margin opposed to deeply curved dactylus. This is the second new species of Epigodromia McLay, 1993 discovered in Indian waters, it raises the species number 11.

Three new brachyuran crab species are described from coral rubble and sponges collected in the southern Indian state of Tamil Nadu. The epialtid, Acanthophrys keeae n. sp., was obtained from coral rubble and is the first species from the genus reported from the Indian Ocean. It is most similar to A. costatus Griffin & Tranter 1986, from eastern Australia, but can be distinguished by the proportionately longer postorbital spine, more strongly granulated gastric region, relatively less inflated and narrower branchial region, sinuous outer margin of the basal antennal article which has the median part concave, almost smooth merus of the cheliped, more elongate male anterior thoracic sternum, more triangular male pleon, and the distal two-thirds of the male first gonopod being almost straight. The pilumnid, Latopilumnus ajmali n. sp., was found in the sponge, Callyspongia (Cladochalina) diffusa (Ridley, 1884), and is characterised by its carapace and pereiopods being covered by a relatively dense coat of short setae with only scattered simple long setae, and the dorsal carapace surface being almost smooth with the regions poorly demarcated. Vellumnus intonsus n. sp. (Pilumnidae) was present in coral rubble, is morphologically most similar to V. penicillatus (Gordon, 1930) (Hong Kong) and V. pygmaeus Takeda, 1977 (Japan) but can be separated by the lateral lobule of the front being separated from the frontal lobes by a deep cleft, the more prominently convex supraorbital margin, triangular external orbital tooth, presence of larger granules on the cheliped carpus and chela, and the distal part of the male first gonopod is proportionately stouter and distinctly hooked.

Nine species of fiddler crabs (Crustacea: Ocypodidae: Gelasiminae) are known from the Arabian Sea and adjacent waters (Red Sea, Gulf of Aden, Gulf of Oman and Arabian/Persian Gulf): five species of Austruca, one Cranuca, two Gelasimus and one Tubuca. COI sequence data match morphological species boundaries and shows high connectivity within each. The fauna is highly endemic, with three species of Austruca (A. albimana, A. iranica and A. sindensis) confined to this region, and four others restricted to the Indian Ocean. restricted to the Indian Ocean. Austruca albimana and A. iranica speciated locally and now have narrowly overlapping ranges in Oman. Our results confirm the westernmost distributions of Austruca annulipes and Tubuca alcocki are Pakistan and the Red Sea, respectively. A key for the nine species is also provided to help identification.

A new pseudocryptic species of the varunid crab genus Pseudohelice Sakai, Turkay & Yang, 2006, is described from India based on morphological and molecular evidence. The new species was collected from higher intertidal zones in the Vellar River estuary, Tamil Nadu, southeastern India, in a habitat composed of muddy and sandy sediment. Pseudohelice annamalai n. sp. is similar to P. subquadrata (Dana, 1851) and P. latreillii (H. Milne Edwards, 1837) in general form, but can be distinguished from the congeners by the characters of the infraorbital ridges, male first gonopod, and female vulvae. In addition, the mitochondrial cytochrome oxidase subunit I sequences also support the new species. The occurrence of Pseudohelice from India links the distribution gap between the western Indian Ocean and western Pacific Ocean. The new species provides additional evidence for the geographic isolation of the eastern Indian Ocean for some marine organisms.

Charybdis (Archias) hongkongensis Shen, 1934 was collected from the Indian coast of the Bay of Bengal and this is the first record from Indian waters. The distinct key characters of this species are: a relatively more produced last antero-lateral tooth, strongly convergent postero-lateral margins, and a smooth, rounded, reduced apex of the male first gonopod. This is the ninth member of Charybdis (Archias) Alcock, 1899 from Indian waters. The species is diagnosed and figured herein.

The monotypic xanthid crab genus Pulcratis Ng and Huang, 1997, previously known only from the South China Sea, is recorded for the first time in the Indian Ocean. The new material was collected by commercial trawlers fishing off the coast of Tamil Nadu state, in southeastern India, and represents a new species, herein described. Pulcratis amabilis n. sp. is similar to the only other congener and type species, P. reticulatus Ng and Huang, 1997, in the general form and fresh coloration, but differs mainly in the outline of the carapace, and morphology of the chelipeds, and the male pleon and gonopods. The subfamilial classification of Pulcratis within Xanthidae is also discussed.