Clistocoeloma villosum (A. Milne-Edwards, 1869 )

Ng, Bee Yan Lee Ngan Kee & Ng, Peter K. L., 2023, On the identities of the sesarmid crabs, Sesarma villosum A. Milne-Edwards 1869, and Clistocoeloma suvaense Edmondson, 1951, with the description of a new species from the West Pacific (Decapoda, Brachyura, Thoracotremata), Zootaxa 5318 (2), pp. 217-236 : 218-220

Clistocoeloma villosum (A. Milne-Edwards, 1869)

( Figs. 1A–C , 5A, B , 6D , 9A–D )

Sesarma villosum A. Milne-Edwards, 1869: 31 [type locality: Upolu , Samoa].

Sesarma villosa — De Man 1887: 644, 645.

Sesarma (Sesarma) villosa — De Man 1897: 153–161 (in part).— De Man 1898: 702 (list) (in part), pl. 29 fig. 30b–d, 30dd.

Sesarma (Holometopus) villosa — Tesch 1917: 208–210 (in part).

Sesarma (Holometopus) villosum — Rathbun 1907: 35.— Crosnier 1965: 56 (in part).—Serène 1968: 107 (list)— Rahayu & Takeda 2000: 40.

Clistocoeloma suvaense — Edmondson 1951: 238, 242 (in part) [not Clistocoeloma suvaense Edmondson, 1951 ].

Sesarma villosum — Ng & Liu 1999: 229.

Clistocoeloma villosum — Davie 2002: 221 (in part).— Ng et al. 2008: 220 (list).— Lee et al. 2013: 420.— Li et al. 2019: 1211 (in part), 1214 (in part).

Type material. Lectotype: male (18.6 × 17.0 mm) ( ZMH K4188 ), Upolu , Samoa, no other data.

Diagnosis. Carapace subquadrate, nearly as wide as long; postfrontal lobes distinct, divided by longitudinal grooves, median pair broad, prominent, distal pair less distinct, not divided ( Fig. 1A ). Inner orbital angle distinct, rounded, with convex outer margin, gap absent between tip of inner orbital angle and frontal margin ( Fig. 1C ). Anterolateral margin of carapace straight, smooth, external orbital angle less pronounced; posterolateral margin slightly convex. Chelipeds dorsal surface of dactylus of chela with 16 evenly spaced tubercles, proximal tubercles small, increasing in size medially, decreasing in size distally ( Fig. 5A ), each tubercle on dorsal surface of movable dactylus with small median chitinous granule ( Fig. 5A ). Single longitudinal pectinated ridge with 27–30 chitinous comb-like tubercles on dorsal surface of chela, distal end of ridge with granules; row of 8 granules behind pectinated ridge on ventral surface of palm ( Fig. 5A ); inner surface of palm granulated, with single vertical row of 8 granules in adult males ( Fig. 5B ). P5 merus relatively short, wide, merus length approximately 0.44 times width ( Fig. 6D ). G1 slightly curved, distal region slightly wide; chitinous tip relatively wide, short; tip with dense tufts of setae, single row of plumose setae on exterior margin; chitinous tip visible when denuded ( Fig. 9A–D ).

Description. Carapace subquadrate, nearly as wide as long; covered with coat of short setae, among which stands small tufts of setae resembling tubercles; carapace smooth when denuded. Postfrontal lobes distinct, divided by longitudinal grooves, median pair broad, prominent, distal pair less distinct, not divided ( Fig. 1A ). Inner orbital angle distinct, rounded, with convex outer margin, no gap present between tip of inner orbital angle and frontal margin ( Fig. 1C ). Anterolateral margin of carapace straight, smooth, external orbital angle less pronounced; posterolateral margin slightly convex. Entire margin of carapace covered with dense, short setae.

Antenna short. Antennular fossa transverse. Third maxilliped with merus rounded. Epistomal margin narrow ( Fig. 1C ).

Chelipeds equal or subequal in size; large, robust in adult male; outer surface of palm smooth when denuded; dorsal surface of carpus covered with small tufts of setae resembling tubercles, smooth when denuded; dorsal surface of dactylus of chela with 16 evenly spaced tubercles, proximal tubercles small, increasing in size medially, decreasing in size distally ( Fig. 5A ), each tubercle on dorsal surface of movable dactylus with small median chitinous granule ( Fig. 5A ); single longitudinal pectinated ridge with 27–30 chitinous comb-like tubercles on dorsal surface of chela, distal end of ridge with granules; row of 8 granules behind pectinated ridge on ventral surface of palm ( Fig. 5A ); inner surface of palm granulated, with single vertical row of 8 granules in adult males ( Fig. 5B ).

P2–P5 covered with dense coat of setae, with small tufts of setae resembling tubercles, longer setae on dorsal and ventral margins of entire leg except dactylus; dactylus shortest, with sharp tip ( Fig. 1A ); P5 merus relatively short, wide, merus length approximately 0.44 times of width ( Fig. 6D ).

Male thoracic sternum covered with short setae, smooth when denuded; sternites 1 and 2 fused, with suture between fused sternites 3 and 4; sternopleonal cavity extends to edge of sternites 1 and 2. Male pleon short, wide, long setae fringed margins of pleon; somite 3 widest; telson slightly broad, triangular with convex margins, rounded tip ( Fig. 1B ); male pleonal locking mechanism absent, without tubercle on sternite 5.

G1 slightly curved, distal region slightly wide; chitinous tip relatively wide, short; tip with dense tufts of setae, single row of plumose setae on exterior margin; chitinous tip visible when denuded ( Fig. 9A–D ). G2 shorter than G1, slightly curved, tip rounded.

Female characters not known.

Remarks. The original description by A. Milne-Edwards (1869) was inadequate by modern standards and no figure was provided. He did not indicate how many specimens he had but the measurements for one specimen from Upolu was listed; no type was designated. Subsequently, De Man (1879) mentioned that the male specimen from the “Museum zu Hamburg ” was send to him by Dr. Pfeffer to examine, and that it is the “Original-Exemplar” of A. Milne-Edwards from Upolu. De Man (1898: pl. 29, fig. 30b–d) subsequently figured the chela of this male specimen. Crosnier (1965: 56) incorrectly assumed that the type was in Paris when he commented that “le type S. villosum , qui devrait se trouver au Muséum national d’Histoire naturelle de Paris, paraît avoir disparu”.

The present type specimen matches the descriptions, measurements and figures provided by A. Milne-Edwards (1869) and De Man (1879, 1898) very well and we are confident that it is the type of S. villosum A. Milne-Edwards, 1869 . As we are not sure if A. Milne-Edwards (1869) had only one specimen, the specimen we have on hand is considered syntypic and is here designated the lectotype. One of the old labels with the specimen states that the lectotype specimen was from the Godeffroy Museum. Based on the eight sales catalogues of Godeffroy Museum that were published between 1864 and 1881 by curator J.D.E. Schmeltz, the species was listed once in catalogue V in 1874 (see Bieler & Petit 2012). The Godeffroy Museum catalogue number of the specimen listed, Sesarma villosa , (see Schmeltz 1874: 76) matches the catalogue number on the label for the lectotype of C. villosum .

Tesch (1917) noted that Sesarma (Holometopus) villosum might be a species of Clistocoeloma because of the pattern of setae described for the species, although he did not formally transfer it there. Serène (1968) listed the species under Sesarma (Holometopus) while indicating that there is a photographed specimen in the “Institute of Oceanography of Nhatrang, Vietnam ”. The actual locality and collection information for the photographed specimen from the collection in the Vietnamese institute is not known and its identity cannot be confirmed. Ng & Liu (1999) noted that S. villosum should be in the genus Clistocoeloma but did not provide any explanation. Sesarma villosum was then briefly discussed by Rahayu & Takeda (2000: 40) before Davie (2002: 221) formally transferred the species to Clistocoeloma , citing McNeill’s suggestion (1968: 79). Komai et al. (2004: 41, 42) briefly discussed the generic assignment of this species in Clistocoeloma , following Davie (2002: 220).

This species has been widely recorded from the IWP, i.e., Sumatra ( De Man 1897, 1898), Caroline Islands ( Rathbun 1907), New Guinea ( Tesch 1917), Philippines ( McNeill 1968), Taiwan ( Li et al. 2019), Japan ( Komai et al. 2004; Yuhara et al. 2017; Takakura & Komai 2019), and South Korea ( Lee et al. 2010), but comparison of the morphology of the specimens from these localities shows that these specimens are of a different species, and is here described as new (see Clistocoeloma nobile n. sp.)

Records of C. villosum from Nosy Be, off Madagascar ( Crosnier 1965; Lenz 1910), Tuléar, Madagascar ( Crosnier 1965), and Kenya ( Schubart et al. 2006) are shown to be a different species. Various specimens from that region have been examined and the species clearly differs from C. villosum , and is more similar in morphology to C. suvaense and C. nobile n. sp. The morphological differences are also supported by DNA sequence differences (unpublished data) and the new species will be described in a separate study by the first author together with S. Cannicci (pers. comm.).

Ecological notes. Little is known about this species except that the specimens were collected from mangroves.

Distribution. Known for certain only from Upolu, Samoa (type locality).

Figures

FIGURE 1. Clistocoeloma villosum (A. Milne-Edwards, 1869), lectotype male (18.6 × 17.0 mm) (ZMH K4188), Samoa. A, overall dorsal view; B, overall ventral view; C, frontal view of carapace.

FIGURE 5. A, B, Clistocoeloma villosum (A. Milne-Edwards, 1869), lectotype male (18.6 × 17.0 mm) (ZMH K4188), Samoa; C, D, C. suvaense Edmondson, 1951, male (18.8 × 16.9 mm) (ZRC 2022.0985), Fiji; E, F, C. nobile n. sp., holotype male, (15.3 × 12.7 mm) (ZRC 2022.0970), Singapore.A, C, E, right cheliped top view; B, D, F, right cheliped ventral view.

FIGURE 6. P5 dorsal view. A–C, Clistocoeloma suvaense Edmondson, 1951; A, holotype male (21.0 × 18.8 mm) (BPBM 3976), Fiji; B, male (18.8 × 16.9 mm) (ZRC 2022.0985), Fiji; C, male (16.2 × 14.3 mm) (ZRC 1973.11.2.490), Samoa; D, C. villosum (A. Milne-Edwards, 1869), lectotype male (18.6 × 17.0 mm) (ZMH K4188), Samoa; E–K, C. nobile n. sp.; E, holotype male, (15.3 × 12.7 mm) (ZRC 2022.0970), Singapore; F, paratype male (15.0 × 13.0 mm) (ZRC 2002.0155) Singapore; G, male (16.0 × 13.5 mm) (ZRC 2022.0977), Vietnam; H, male (17.4 × 14.9 mm) (ZRC 2022.0973), Philippines; I, male (17.3 × 15.0 mm) (ZRC 2022.0994), Hong Kong; J, male (18.2 × 15.0 mm), Japan; K, male (16.2 × 14.2 mm) (WS898), Korea.

FIGURE 9. Left G1. A–D, Clistocoeloma villosum (A. Milne-Edwards, 1869), lectotype male (18.6 × 17.0 mm) (ZMH K4188), Samoa; E–H, C. suvaense Edmondson, 1951, holotype male (21.0 × 18.8 mm) (BPBM 3976), Fiji. A, E, dorsal view; B, F, left lateral view; C, G, ventral view; D, H, right lateral view. Scale bar = 1 mm.