Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891

Ng, Peter K. L., Priyaja, P., Kumar, A. Biju & Devi, S. Suvarna, 2019, 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), ZooKeys 818, pp. 1-24 : 4-6

Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891

Nectopanope Anonymous, 1891: 56 (nomen nudum).

Nectopanope Wood-Mason in Wood in Wood-Mason & Alcock, 1891: 261.

Diagnosis.

Carapace (Fig. 3A, B) subhexagonal, wider than long, dorsal surface smooth, regions poorly indicated; front (Fig. 3 C–E) wide, straight with small median notch, with transverse sulcus along margin. Anterolateral borders (Fig. 3A, B) convex; with two low teeth posterior to broadly triangular outer orbital angle, first tooth wider than acute second tooth. Orbits (Fig. 3 C–E) wide, spherical, deep; supraorbital margin with submedian notch, small acute lobe before notch with front; low suborbital tooth on broad, suborbital border; eye peduncles short, stout, with large subreniform (dorsoventrally flattened) cornea (Fig. 36D, E). Basal antennal article mobile, completely closing orbital hiatus (Fig. 3D). Ischium of third maxilliped (Fig. 3B) elongate; anteroexternal margin of merus auriculiform. Cheliped fingers (Figs 3A, G, 4E, F) stout, as long as propodus, not pigmented; carpus with small, sharp spine on inner margin, merus with acute anterodorsal tooth. Dorsal margins of ambulatory legs (P2-P5) (Figs 3A, 4 G–J) meri, carpi, propodi unarmed, dactyli slender, smooth, setose; P5 propodus, dactylus proportionally short, flattened, fringed with many short setae. Thoracic sternum (Fig. 4A, D) relatively wide; sternites 1, 2 completely fused; suture 2/3 complete, gently convex towards buccal cavity; sternites 3, 4 medially fused, with shallow median groove, almost indiscernible with only lateral notch distinct; sutures 4/5, 6/7, 7/8 medially interrupted, 5/6 complete; median groove on thoracic sternites 7, 8. Male sternopleonal cavity (Fig. 4A, D) deep, reaching median part of sternite 4, just before sternite 3. Press-button of male pleonal-locking mechanism (Fig. 4D) present as low tubercle on sternite 5, near thoracic suture 4/5. Male pleon (Fig. 4 A–C) narrow, slender, T-shaped, lateral margins of somites 4-6 abruptly narrowing from somite 3 to transversely narrow, acutely triangular telson (Fig. 4B); somite 3 wide, reaching inner margins of P5 coxae; no part of thoracic sternite 8 exposed by closed pleon, somite 2 transversely shorter than somite 3, somite 1 (Fig. 4C) conspicuous, narrow. G1 (Fig. 7 A–D) long, slender, almost straight; distal quarter distinctly chitinised; apex sharp, distal third with numerous sharp denticles. G2 (Fig. 7E) less than one-third G1 length, relatively straight, apex spatuliform. Male genital opening (gonopore) coxal; penis long. Female characters not known.

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) repeated the same comments in his treatment of the deep-sea Crustacea of the Indian Seas. Nectopanope longipes Wood-Mason in Wood-Mason & Alcock, 1891, is now generally regarded as a valid species in Carcinoplax H. Milne Edwards, 1853 ( Goneplacidae MacLeay, 1838) (see Castro 2007).

Nectopanope Wood-Mason in Wood-Mason & Alcock, 1891, was originally placed in Cancridae Latreille, 1802, by Wood-Mason (in Wood-Mason and Alcock 1891) with Alcock (1898, 1899a) later transferring the genus to Xanthidae s. lato. Alcock (1898) recognized a new group in his xanthid subfamily Pilumninae , Heteropanopioida Alcock, 1898, in which he included Heteropanope Stimpson, 1858, Eurycarcinus A. Milne-Edwards, 1867, and Nectopanope . 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).

The carapace anterolateral margin of Nectopanope has three distinct teeth (Figs 2, 3A, C) (with only two teeth in Psopheticoides , with the external orbital tooth very broad; Sakai 1969: text-fig. 16b; Sakai 1976: pl. 192, fig. 3). The external orbital tooth of Psopheticoides , however, is usually partially medially indented, and although the cleft is not deep, it gives the appearance of having three teeth on the anterolateral margin (cf. Sakai 1969: text-figs 16b, 18b; Sakai 1976: text-fig. 282a; Castro and Ng 2010: fig. 36A). The frontal margin in Nectopanope is medially indented (Figs 2, 3A, C) (margin entire in Psopheticoides ; cf. Castro and Ng 2010: fig. 36A); the ischium of the third maxilliped is proportionately longer with the auriculiform anteroexternal angle of the merus more developed (Fig. 3B) (ischium of third maxilliped relatively shorter and the anterexternal angle of the merus less produced in Psopheticoides ; cf. Castro and Ng 2010: fig. 36C); the cornea is weakly reniform (Fig. 3D, E) (cornea prominently reniform in Psopheticoides ; cf. Castro and Ng 2010: fig. 36B); the male telson is proportionately shorter (Fig. 4A) (elongated and linguiform in Psopheticoides ; cf. Castro and Ng 2010: fig. 36E); and the G1 is relatively straighter with the tip tapered to a tip (Fig. 7 A–D) (G1 slightly sinuous with the tip arrow-shaped in Psopheticoides ; cf. Castro and Ng 2010: fig. 38D, E).