A collection of crabs (Crustacea, Brachyura) from the southwestern coast of India, with a discussion of the systematic position of Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891 (Euryplacidae)

Abstract A report on the brachyuran crabs collected from the southwestern coast of India by the Indian research vessel FORV Sagar Sampada is presented. The material consists of 13 species from three genera and five families, of which four are new records for India: Heteroplaxmaldivensis (Rathbun, 1902) (Euryplacidae), Cryptopodiacollifer Flipse, 1930 (Parthenopidae), Thalamitamacrodonta Borradaile, 1903 (Portunidae), and Paraxanthodescumatodes (MacGilchrist, 1905) (Xanthidae). The cruise also obtained the first known male of Nectopanoperhodobaphes Wood-Mason in Wood-Mason & Alcock, 1891 (type species of Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891), and its characters show that it is in fact a member of the Euryplacidae Stimpson, 1871. The genus had previously been incorrectly classified in the Xanthidae MacLeay, 1838.


Introduction
We here report on a small but noteworthy collection of brachyuran crabs obtained by a fishery research vessel off the southwestern coast of India in 2017. While consisting of only 13 species from three genera and five families, the material obtained includes several rare species, including one which has not been seen since 1891.
The discovery of a male of Nectopanope rhodobaphes Wood-Mason in Wood-Mason & Alcock, 1891, is significant as the family position of the genus Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891, has been uncertain, because it was previously known only from the type female. The male characters show that Nectopanope is a member of Euryplacidae Stimpson, 1871, and close to Psopheticoides Sakai, 1969, from the western Pacific. Nectopanope is rediagnosed, while Nectopanope rhodobaphes is redescribed and figured. A male of the rarely reported parthenopid Cryptopodia collifer Flipse, 1930, not previously known from India, is figured. The euryplacid Heteroplax maldivensis (Rathbun, 1902), the rarely reported portunid Thalamita macrodonta Borradaile, 1903, and the xanthid Paraxanthodes cumatodes (MacGilchrist, 1905), are also recorded from India for the first time.

Materials and methods
All specimens were collected during an exploratory survey (cruise 360) of FORV Sagar Sampada belonging to the Center for Marine Living Resources & Ecology (CMLRE) under the Ministry of Earth Sciences, India, in May 2017, conducted along the southwestern coast of India. Specimens were collected using grabs and dredged from depths ranging from 50-200 m. The material studied is in the museum collections of the Department of Aquatic Biology and Fisheries, University of Kerala (DABFUK).
Measurements provided are of the maximum carapace width and length, respectively. The classification and terminology used follows Ng et al. (2008) and Davie et al. (2015a, b). Complete synonymies are only provided for species which are treated at length.

Family Raninidae De Haan, 1839 Notosceles Bourne, 1922
Notosceles serratifrons (Henderson, 1893)  Remarks. Henderson (1893) described this species from Sri Lanka. It has since been found in India (Alcock 1896;Dev Roy 2013;Trivedi et al. 2018) as well as Australia, Japan, mainland China and Taiwan (Sakai 1976;Chen and Sun 2002;Ahyong et al. 2009  Remarks. The species was first described from the Andaman Sea (Alcock 1896) and has since been reported from other parts of India, Southeast Asia, China, and Japan (Sakai 1976;Serène and Soh 1976;Tan 1996;Chen and Sun 2002;Dev Roy and Nandi 2012).

Thalamita Latreille, 1829
Thalamita macrodonta Borradaile, 1902  Remarks. Borradaile (1902) described Thalamita exetastica macrodonta from two specimens from two islands in the Maldives, Kolumadulu and Suvadiva. Crosnier (1975) examined the syntypes and commented that the two specimens are not conspecific. He noted that the specimen from Kolumadulu Island was almost certainly T. sexlobata Miers, 1886, while the other from Suvadiva Island is the actual T. macrodonta which he treated as a distinct species. Apel and Spiridonov (1998) re-examined the type material and selected the second syntype from Suvadiva as the lectotype of T. macrodonta s. str.
The present specimen from India is incomplete and not in good condition, but agrees with the description and figures of T. macrodonta by Crosnier (1975: fig. 4c, d) and Apel and Spiridonov (1998: fig. 59).
Remarks. The type species of Nectopanope has been somewhat confused. Only one species, Nectopanope longipes, was recognised in Anonymous (1891: 56) but both these names are nomina nuda. Wood-Mason (in Wood-Mason and Alcock 1891: 261, 262) provided valid descriptions for the genus and species, and included N. rhodobaphes as a second species. Ng et al. (2008: 80) noted that the type species of Nectopanope was N. rhodobaphes by monotypy, but this is not correct. Although Wood-Mason (in Wood-Mason and Alcock 1891) did not explicitly state which was the type species for Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891, they wrote "Nectopanope rhodobaphes, gen. et sp. n., Wood-Mason" (Wood-Mason in Wood-Mason and Alcock 1891: 261). Under Article 68.2.1 of the Code (ICZN 1999), this is sufficient to recognise it as the type species of the genus (see Huys et al. 2014: 27). Alcock (1898: 213) later commented that Nectopanope should be restricted to N. rhodobaphes and that "Nectopanope longipes, which was provisionally referred to this genus by Wood-Mason, who had insufficient material for examination, turns out, now that numerous good specimens have been dredged by the 'Investigator,' to be a Catometope belonging to the genus Carcinoplax." Alcock (1899a: 64) Ng et al. (2008: 204) transferred Nectopanope to Xanthinae (Xanthidae) without explanation. This was necessary as Heteropanope and Eurycarcinus had already been moved to the Pilumnidae (present Pilumnoidea) by then (see Ng et al. 2018).
The family position of Nectopanope is difficult because its only species, N. rhodobaphes, has previously only been known from one female specimen. Wood-Mason (in Wood-Mason and Alcock 1891: 262) noted that he had "one specimen obtained at Station 96, 98 to 102 fathoms; the length of its carapace is 21.4 millim., and the greatest breadth between the points of the third teeth 29 millim." Station 96 was in the Bay of Bengal, 18°30'N, 84°46'E, substrate is sand at a depth of 98-102 fathoms, and dated 4 March 1890 (Anonymous 1914). The sex of the specimen was not stated. Alcock (1899a: pl. 38 fig. 6) figured the specimen but it is not clear what its sex was (Fig. 2). Alcock (1898: 213;1899a: 65) noted that they only had one female collected from the Godávari coast (in the Bay of Bengal) from 98-102 fathoms, that is the type. A search in the Zoological Survey of India in Calcutta for this specimen was not successful and it could not be located (S. Mitra, personal communication).
The study of the present male specimen resolves the systematic position of Nectopanope. The structures of the male pleon and gonopods leave no doubt that Nectopanope is in fact a member of Euryplacidae Stimpson, 1871. Nectopanope is only superficially resembles Eurycarcinus (and the Pilumnidae) due to similar carapace features. Their male pleons and gonopods, however, are completely different (cf. Ng et al. 2018).
In Euryplacidae, the general shape and structure of the carapace as well as smoothness of the surfaces of Nectopanope most closely resembles Psopheticoides Sakai, 1969 (with only one species, P. sanguineus Sakai, 1969), from the western Pacific. They also share a similar eye morphology. The eye of Psopheticoides is large and is distinctly flattened dorsoventrally, with the structure appearing reniform (Castro and Ng 2010: fig. 36B). The eye of Nectopanope is relatively less distinctly flattened dorsoventrally and only weakly reniform in shape (Fig. 3D, E). No other euryplacids, however, have such a distinct eye structure which has been reported in other deep-sea brachyurans (e.g., Hexaplax Doflein, 1904, Hexapodidae; cf. Rahayu and Ng 2014).
Chelipeds (P1) (Figs 3A, G, 4E, F) unequal, right chela slightly larger; fingers slender, as long as palm; dorsal margin of palm rounded; distal half of chela with ventral margin (including entire pollex) possessing distinct subventral longitudinal sulcus, forming subcristiform ventral margin; outer surface of palm smooth; inner surface smooth with gently convex median part, ventro-proximal part with low lobiform rounded projection; cutting edge of pollex of major chela with prominent large triangular teeth; dactylus gently curved with 2 shallow longitudinal median sulci on outer margin (upper one deeper), cutting edge with large triangular teeth; fingers of minor chela similar to those on major chela.
Remarks. The colour of the fresh type specimen was described as "a beautiful deepsea pink, with a dotted, V-shaped, white mark between the gastric and branchial regions." (Wood-Mason in Wood-Mason and Alcock 1891: 262). The present preserved specimen, although faded, retains enough colour to suggest that in life, it had the colour and pattern described in the original description. This colour is somewhat similar to that known for Psopheticoides sanguineus which is red to pinkish-red all over but with a white ring on the median dorsal surface (Sakai 1976: pl. 192, fig. 3;Castro and Ng 2010: fig. 39C).
The type female (Fig. 2) shows the branchial regions distinctly swollen but this is probably due to parasites, although the specimen was not dissected. This has precedence in the Australian euryplacid Eucrate sexdentata Haswell, 1882, in which one specimen has both sides of the branchial regions swollen and infected by bopyrids (cf. Castro and Ng 2010: fig. 10E).
The present specimen is clearly H. maldivensis as redescribed and figured at length by Castro and Ng (2010: 61). The species was previously known only from the holotype male (7.4 × 4.8 mm) obtained from Gan Island in Addu Atoll in the Maldives. The present male differs from the type male in having the frontal margin slightly more sinuous and the cleft between the external orbital tooth and the anterolateral tooth is more U-shaped (Fig. 5A, B) (versus frontal margin almost straight and the lateral carapace cleft being V-shaped in the holotype; cf. Castro and Ng 2010: fig. 22A); and while the G1 shape is similar, the distal spination is relatively less pronounced and the tip is sharply tapering (Fig. 7F, G) (versus distal half with relatively more spines and the tip is subtruncate in the holotype; cf. Castro and Ng 2010: fig. 24D, E). The differences are not substantial and can easily be explained by variation and size, the present male (9.9 × 6.3 mm) being larger than the type (7.4 × 4.8 mm). Castro and Ng (2010) showed that records of "H. nitida" from the Andaman Sea should be referred to a new species, H. pilimenes; and indicated that true H. nitida should be restricted to East Asia. The records of "H. nitida" from the Gulf of Martaban (south of Myanmar) and off Madras in India by Henderson (1893: 379) are almost certainly not this species. The Myanmar material is probably H. pilimenes, while that from India may be this species or even H. maldivensis instead. Specimens will need to be re-examined to be certain.
Heteroplax maldivensis is thus far known for certain only from the Maldives (Rathbun 1902;Castro and Ng 2010) and the present specimen represents the first confirmed presence of this species in India. Remarks. This species was described from off Sri Lanka and Andamans by Alcock (1895) and has since been reported from Mauritius and Japan (Flipse 1930;Michel 1964;Sakai 1976). Ng and Rahayu (2010) figured the syntypes of the species.
The present materials are all juveniles, with none of the gonopod structures of the males developed even though the chelipeds are elongated. The pronounced "neck-like" constriction in adults of this species has still not developed (Fig. 6B).
The lateral margins of the rostrum are straight in the holotype of C. collifer (cf. Chiong and Ng 1998: fig. 22A) but are gently convex in the present male (Fig. 6C), as was figured by Shen et al. (1982: pl. 1 fig. 8) for the Chinese specimen. The male telson of C. collifer is semi-circular in shape (Fig. 6D), and is distinct from the more triangular shapes of other Cryptopodia species (see Chiong and Ng 1998). The G1 structure of C. collifer is most similar to that of C. pan Laurie, 1906, from the Indo-West Pacific (cf. Chiong and Ng 1998: fig. 24A, B, D-K), but the latter species is easily distinguished by its third maxilliped being distinctly swollen (Chiong and Ng 1998: fig. 23C). The third maxilliped of C. collifer, like those of other congeners, is quadrate and not inflated (Fig. 6D).  (Rathbun, 1902), male (9.9 × 6.3 mm) I-M Cryptopodia collifer Flipse, 1930, male (17.5 × 10.6
We refer the present specimen to P. cumatodes, described from the western Indian Ocean by MacGilchrist (1905), with doubt because of its relatively small size. It differs from typical P. cumatodes (see Alcock et al. 1907: pl. 79, fig. 1, 1A;Guinot 1968: fig. 60;Serène 1984: pl. 30C; fig. 1D-F) in having the carapace proportionately less broad, the grooves and ridges on the dorsal carapace surface less prominent and the grooves on the thoracic sternum relatively shallower (Fig. 6G, H). The G1 of the present specimen is developed and its structure agrees relatively well with that figured by   fig. 2E, G-I) for P. cumatodes, except that the distal half is more gently curved and the distal setae less dense (Fig. 7N, O).