First record of the deep-water xanthid crab genus, Pulcratis Ng & Huang, 1997, from the Indian Ocean, with description of a new species (Crustacea: Brachyura: Xanthidae)

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.

Pulcratis n. sp. from eastern Indian Ocean Nauplius, 28: e2020010 south-eastern coast of India, in the Bay of Bengal. These trawlers land both commercially important catch and relatively low-value bycatch (consisting of brachyuran crabs and other decapod crustaceans) in the Pazhayar fish port, Nagapattinam district, Tamil Nadu state. Some recent work on deep-water brachyurans, including descriptions of new taxa, have been made possible from material collected from this port, contributing to a better understanding of the regional diversity of brachyurans in India (Ng et al., 2017a;2017b;Prema et al., 2017;2019). After detailed morphological comparisons with the type material and other material of P. reticulatus, the Indian specimens are considered to be a new species and are described herein. The subfamilial classification of Pulcratis within the family Xanthidae is also discussed in light of recent developments in the understanding of evolutionary relationships among xanthid crabs.

MaTerial and MeThods
Material examined is deposited in the Centre of Advanced Study in Marine Biology, Annamalai University, Parangipettai, Tamil Nadu, India (CASAU); and the Zoological Reference Collection of the Lee Kong Chian Natural History Museum, National University of Singapore (ZRC). Measurements provided, in millimetres (mm), are of the maximum carapace width and the carapace length at the midline. The following abbreviations are used: G1, G2 = first and second male pleopods, respectively; P1-P5 = first to fifth pereopods, respectively. The nomenclature for the carapace regions follows Dana (1852) (also Serène, 1984 Remarks. The subfamilial placement of Pulcratis in Xanthidae requires further evaluation. Ng and Huang (1997) assigned it to Zosiminae Alcock, 1898(sensu Serène, 1984, primarily due to the cristate margins of the meri of the ambulatory legs, and cited its similarity in general form and color pattern to Paratergatis Sakai, 1965 (type and only species: P. longimanus Sakai, 1965). Jeng and Ng (1998) commented further on the morphological distinctions between Paratergatis and Pulcratis.
Subsequently another new genus, Ovatis Chen, 2004 (type species: O. simplex Ng andChen, 2004;monotypic), was described from the South China Sea. Ng and Chen (2004) considered Ovatis to be closely related to Liagore De Haan, 1833, and assigned it to Xanthinae MacLeay, 1838. They also noted the morphological similarities among the xanthines, Ovatis and Liagore, and the zosimines, Paratergatis and Pulcratis, leading them to note that the only definitive morphological character being used to separate members of the two subfamilies is whether or not the articles of the ambulatory legs are cristate, and even then, there are difficulties in assessing the degree of such cristation. Ng et al. (2008) also pointed out incongruencies in the larval morphology of members of these two groups (see also Ng and Clark, 1994;Clark et al., 2004).
Given the presently available evidence, Pulcratis is tentatively assigned to Xanthinae sensu lato (viz., Ng et al., 2008) pending a revision of this polyphyletic subfamily. Lai et al. (2011: 430, 431) did propose some diagnostic characters for the xanthine clade (Xan 2) to which Pulcratis belongs: "The characters that define this clade are the presence of distinct longitudinal rows of dense setae on the dactylus of all four ambulatory legs, a broad male thoracic sternite 7, abdominal somites 1 and 2 broad; male thoracic sternite 8 just visible when abdomen is closed, episternites 5-7 delimited by a sulcus, and coxo-sternal condyle of P5 inserted between abdominal somites 2 and 3. " Not all of these characters, however, can be observed in Pulcratis. In particular, the episternites 5-7 do not have sulci separating them from their respective thoracic sternites. The xanthid crab group, 'tribe Liagorini' (viz., Števčić, 2005) may be an available name for this clade (i.e., perhaps as subfamily Liagorinae), but the formal action required is not part of the scope of this current paper, as the proper taxonomic ranking and morphological diagnosis can only be made in the context of a familywide revision and after sufficient examination of a large number of related taxa.
Etymology. The specific epithet "amabilis", L. lovely (adj.), is used, alluding to the beautiful pattern of the fresh colouration of the new species.
Color in life. Base color off-white, interspersed with orange, both forming reticulated patterns on carapace and chelipeds; fingers of chela off-white. Orange splotches on off-white ambulatory legs, forming banded pattern on ambulatory meri, carpi, and propodi. Ventral and internal surfaces off-white (Fig. 4). Live coloration very similar to that of P. reticulatus (cf. Ng and Huang 1997: fig. 8D, E).
Pulcratis amabilis n. sp. is the first representative of the genus to be recorded from the Indian Ocean, the only other species of the genus, P. reticulatus, being found in the South China Sea. Currently, the new species is only known from the waters off the coast of southeastern India (Tamil Nadu) in the Bay of Bengal, eastern Indian Ocean, and occurring at depths of 50-100 m on muddy to silty bottoms.

aCKnowledgeMenTs
The authors would like to thank Peter K. L. Ng (National University of Singapore) for facilitating this collaborative work. The second author (PM) sincerely thanks the University Grants Commission (UGC), New Delhi, India, for the PhD Fellowship (BSR-BININ00449691). The third author's (SR) visit to the Lee Kong Chian Natural History Museum (LKCNHM), Singapore, was made possible through a LKCNHM Visiting Fellowship. PM and SR are also grateful to the administrations of the Annamalai University, India, and the Loven Center for Marine Infrastructure, Kristineberg, Sweden, for the constant encouragement and support. The authors are grateful for the constructive comments of Peter Ng and Paul Clark which helped to improve this paper.