Cryptopilumnus, Hsueh & Huang & Ng, 2009

Hsueh, Pan-Wen, Huang, Jung-Fu & Ng, Peter K. L., 2009, On a new genus and new species of pilumnid crab from Taiwan, and the generic placements of Heteropanope changensis (Rathbun, 1909) and Pilumnopeus pereiodontus Davie and Ghani, 1993 (Crustacea: Decapoda: Brachyura), Journal of Natural History 43 (5 - 6), pp. 323-334 : 324-326

Cryptopilumnus gen. nov.

Type species

Cryptopilumnus taiwanensis sp. nov., by present designation.

Diagnosis

Carapace with poorly defined regions; front broadly bilobed; suborbital margin unarmed; orbital hiatus open; supraorbital margin entire; anterolateral margin arcuate, teeth/lobes poorly defined or almost indiscernible, low; posterolateral margins distinctly converging towards posterior carapace margin; outer surface of chelae covered with numerous granules and setae; dactylo-propodal lock present on P2–P5; ischium of P5 with short tubercles ventrally (may be comb-like); ventral margins of P5 with prominent tubercles proximally; thoracic sternites 1–3 completely fused without trace of sutures; all male somites free, completely covering sternite 8 when closed; G1 slender, S-shaped, distally tapering.

Etymology

The name is derived from the Latin for hidden, in combination with the name Pilumnus , alluding to the habits of the type and constituent species. The gender is masculine.

Remarks

Of the 25 genera now recognized in the Pilumninae (Ng et al. 2008) , Cryptopilumnus gen. nov. superficially resembles species in Heteropanope Stimpson, 1858 (type species Heteropanope glabra Stimpson, 1858 ), Pilumnopeus A. Milne-Edwards, 1867 ( Pilumnopeus crassimanus A. Milne-Edwards, 1867 ), and Aniptumnus Ng, 2002 [type species Pilumnus (Parapilumnus) quadridentatus De Man, 1895 ]. This is especially with regard to poorly defined carapace regions, shape of the front, the presence of small granules along the frontal margin, setae covering the palms of the chelipeds, armature on the ventral margins of the ischium and merus of P4 and P5. However, the most important character that separates Cryptopilumnus , new genus, from these genera is the lack of a transverse suture between male thoracic sternites 1 and 2, a feature evident on the other genera (see Davie 1989; Ng 2002; Ng and Clark 2008). The relatively more rounded carapace with low anterolateral teeth or lobes, and the ambulatory merus and ischium armed with tubercles are also distinguishing features.

Two problematic pilumnine species merit comment, A. changensis Rathbun, 1909 , and P. pereiodontus Davie and Ghani, 1993 . Actumnus changensis Rathbun, 1909 was briefly described on the basis of only one female (5.7 by 3.8 mm) collected from coral at a depth of one fathom from the island of Koh Chang in the Gulf of Thailand ( Rathbun 1909, p. 114). Rathbun (1910, p. 357, figures 41, 42) later provided more information and figures and noted that the type female was from a series of three males and two females, all collected at the same time. Only the original female mentioned by Rathbun (1909) can be considered to be type material. The species was transferred to Heteropanope Stimpson, 1858 , by Balss (1933) without much comment. Davie (1989, p. 130) provisionally left it in Heteropanope as one of the three recognized species although he did not have specimens of the species to hand at the time. With regard to P. pereiodontus Davie and Ghani, 1993 , the species was described from two males and one female from Churna Island in Pakistan, but the authors expressed uncertainty about its generic placement because of several unusual characters (i.e. the less protruding frontal lobes, the more strongly tubercular chelipeds and the armature of the fourth ambulatory leg), which are not seen in other members of the genus. Davie and Ghani (1993, p. 65) also commented that ‘‘Because of the apparent strong similarities, the two species [ Heteropanope changensis and P. pereiodontus ] could be considered congeneric and therefore H. changensis should be transferred to Pilumnopeus . The main difficulty with this action is that P. pereiodontus itself does not fully agree with the generic diagnosis of Pilumnopeus given by Davie (1989). The points of departure are that the lateral frontal teeth are almost obsolete, and sternite 8 is not visible laterally beside the closed male abdomen.’’ Peter Davie kindly re-examined the type male specimen of P. pereiodontus at our request. He comments (personal communication) that the thoracic sutures 1–3 are totally fused, and mostly fused to sternite 4 as well, except for clear short lateral incision/sulcus; and sternite 8 is not visible with the abdomen closed. The anterior edge of sternite 8 is also in line with the lateral leading edge of the third abdominal segment, but it is clearly hidden behind this structure.

In the ZRC is a good series of specimens of H. changensis collected in Singapore which agree very well with the descriptions of Rathbun (1909, 1910) ( Figures 1 , 2 , 5E,F ). Although Rathbun (1909, 1910) does not describe the structure of P5, her figure shows the armature on the merus and ischium very well ( Rathbun 1910, figure 41). Comparing these with the detailed descriptions and drawings of P. pereiodontus by Davie and Ghani (1993), we agree with Davie and Ghani (1993) that the two species are very close and clearly congeneric. Both species, however, are also very close to C. taiwanensis . All three species have indistinct regions of the carapace, have a broadly bilobed front, lack a tooth or spine on the suborbital margin, possess low to indistinct anterolateral teeth, have the outer surfaces of the cheliped palms prominently granular and setose, have the ventral margins of the ischia and meri of the P5 armed with tubercles, have thoracic sternites 1–3 completely fused, have the male sternite 8 completely hidden when the male abdomen is closed, and have a triangular telson and a sinuous G1 which is distally tapering ( Table 1). As such, H. changensis ( Rathbun, 1909) and P. pereiodontus Davie and Ghani, 1993 , are here also transferred to Cryptopilumnus .

Interestingly, all three species of Cryptopilumnus apparently live inside non-coral rock. Specimens of C. changensis were collected by the third author from between slabs of soft sedimentary rock in the intertidal zone, in areas with strong wave action. These rocks have numerous deep crevices and cracks in which the crabs live. Cryptopilumnus pereiodontus lives ‘‘in holes and crevices in stones’’ ( Davie and Ghani, 1993, p. 62), although the type of stone was not specified.

Comparative material

Cryptopilumnus changensis ( Rathbun, 1909) , 1 male (5.9 by 4.4 mm), 9 females (5.6– 7.1 by 3.9–4.7 mm; 3 ovigerous) ( ZRC 1970.1.20.32-41), Horsburg Lighthouse (Pulau Pedra Blanca), Singapore , coll. A. Monterio, 1965; 5 males, 6 females (3 ovigerous) ( ZRC 1970.1.20.32), Horsburg Lighthouse (Pulau Pedra Blanca), Singapore , coll. A. Monterio, 10 August 1965; 7 males (2.8–7.3 by 2.2–5.2 mm), 12 females (3.1–5.5 by 2.2–4.1 mm; 9 ovigerous) ( ZRC 1987.475.495), Pulau Kukor , Singapore , coll. P. K. L. Ng, 30 December 1986. Aniptumnus quadridentatus (De Man, 1887) , 1 male (13.82 by 8.89 mm) ( ZRC 1989.3649 - 3660 ), Singapore . Pilumnopeus makiana (Rathbun, 1931) , 1 male (12.71 by 9.23 mm) ( ZRC 2001.0099 ), Hong Kong .

Figures

Figure 1. Cryptopilumnus changensis (after Rathbun, 1910, figures 41, 42). (A) Overall view; (B) right chela; (C) left chela.

Figure 2. Cryptopilumnus changensis, male (4.6 by 3.3 mm) (ZRC 1970.1.20.32). (A) Overall dorsal view; (B) ventral view; (C) outer view of right chela.

Figure 5. (A–D) Cryptopilumnus taiwanensis gen. nov., sp. nov. Holotype male (4.5 by 3.0 mm) (NMNS5771-001). (E, F) Cryptopilumnus changensis, male (4.6 by 3.3 mm) (ZRC 1970.1.20.32). (A, B, E) left G1; (C) distal part of left G1; (D) left G2; (F) right fourth ambulatory leg. Scale bars: A, B, D, E, 0.2 mm; C, 0.1 mm; F, 0.5 mm.