Clistocoeloma nobile Ng & Ng 2023, n. sp.

Clistocoeloma nobile n. sp. (Figs, 2B, C, 5E, F, 6E–K, 7A–C, 8C, D, 11A–D) Sesarma (Sesarma) villosa — De Man 1897: 153–161 (in part).— De Man 1898: 702 (list) (in part), pl. 29 fig. 30a, 30e [not Sesarma villosum A. Milne-Edwards, 1869]. Sesarma (Holometopus) villosum — McNeill 1968: 79 (in part).— Rathbun 1907: 35. Sesarma (Holometopus) villosa — Tesch 1917: 208–210 (in part), 231 (list), 237 (key), 239 (footnote), 260, pl. 17 fig. 2 [not Sesarma villosum A. Milne-Edwards, 1869]. Chiromantes villosum — Nomoto et al. 1999: 9, pl. 1 fig. 6.— Kishino et al. 2001a: 17–18, pl. 2 fig. 2.— Kishino et al. 2001b: 127 (list), table 2.— Shokita et al. 2002: 78 (list), 85, photo 4A–1 fig. A [not Sesarma villosum A. Milne-Edwards, 1869]. Cleistocoeloma (sic) suvaense — Tan & Ng 1994: 82 (list) [not Clistocoeloma suvaense Edmondson, 1951]. Clistocoeloma suvaensis —Wee & Ng 1996: 82 (list) [not Clistocoeloma suvaense Edmondson, 1951]. Clistocoeloma villosum — Davie 2002: 221 (in part).— Komai et al. 2004: 38, 40–42, fig. 1B, 3.— Karasawa et al. 2006: 60, 61, fig. 1. — Schubart et al. 2009: 3 (list), fig. 18 (in part).— Lee et al. 2010: 179–181, fig. 1 A–H.—Maenosono & Sakai 2016: 6, fig. 2D.— Yuhara et al. 2017: [1–4], fig. 2.— Yuhara & Yokooka 2019: 8–11, figs. 2C, 3.— Li et al. 2019: 1208 (list), 1211–1214, figs. 1B, 3. – Takakura & Komai 2019: 25–30, figs. 1–5 [not Sesarma villosum A. Milne-Edwards, 1869]. Clistocoeloma cf. suvaense — Li 2015: fig. 15 [not Clistocoeloma suvaense Edmondson, 1951]. Type material. Holotype: male (15.3 × 12.7 mm) (ZRC 2022.0970), stn SW7 (SS-00221), pontoon at south lagoon, St. John’s Island, Singapore, 1°12.92’N, 103°51.09’E, coll. CMBS II Expedition, 20 May 2013. Paratypes: 1 female (18.7 × 15.2 mm) (ZRC 2022.0971), same locality and collection information as Holotype. — 3 males (16.2 × 13.8 mm, 15.9 × 14.2 mm, 12.6 × 11.0 mm), 1 female (13.2 × 11.2 mm) (ZRC 2002.0154), Kusu Island, Singapore, coll. C.D. Schubart, 15 April 2000. — 1 male (15.0 × 13.0 mm) (ZRC 2002.0155), Sungei Buloh, Singapore, coll. C.D. Schubart & N. Sivasothi, 16 August 1999. — 6 males (16.9 × 14.3 mm, 15.8 × 13.5 mm, 15.2 × 13.1 mm, 15.1 × 13.0 mm), 2 females (15.1 × 12.8 mm, 12.7 × 10.3 mm) (ZRC 2022.0972), Lazarus Island, Singapore, coll. B.Y. Lee et al., 30 September 2018. Other material examined. South Korea: 1 female (12.8 × 10.8 mm) (WS900), Gosan, Jeju Island, coll. J. Jung, May 2003.— 1 female (14.5 × 12.1 mm) (WS899), Gosan, Jeju Island, coll. J. Jung, May 2003.— 1 male (16.2 × 14.2 mm) (WS898), Gosan, Jeju Island, coll. J. Jung, May 2003. Japan: 3 males (18.2 × 15.0 mm, 12.7 × 11.0 mm, 9.4 × 8.1 mm), 1 female (19.0 × 15.8 mm) (ZRC 2022.0990), Yagaji-jima, Okinawa, coll. J.J. Li, 18 July 2016.— 1 damaged female (11.9 × 10.1 mm) (ZRC 1999.0254), Nago City, Yagaji Island, coll. 23 May 1978.— 1 male (9.4 × 8.0 mm) (ZRC 2011.1037), Kumeijima, Okinawa, coll. T. Komai, 16 November 2009.— 1 female (10.3 × 8.8 mm) (ZRC 2011.1036), Ohara, Kumejima, 26°20’57.8”N 126°43’33.9”E, coll. Kumeijima 2009 Expedition, 18 November 2009. Taiwan: 1 ovigerous female (15.8 × 13.4 mm) (ZRC 2022.0991), Xiangjiaowan, coll. J.J. Li, 25 August 2014.— 1 ovigerous female (16.0 × 13.2 mm) (ZRC 2022.0992), Dintanzi, Hengchun Township, Pintung County, coll. Z.C. Ji, 3 September 2017. Hong Kong: 1 male (12.4 × 10.7 mm), 1 female (12.5 × 10.5 mm) (ZRC 2022.0993), To Kwa Peng, Sai Kung, coll. K. Wong, 9 May 2016.— 1 male (17.3 × 15.0 mm) (ZRC 2022.0994), Kak Po, Northeast Hong Kong, coll. C. Cheng & A. Quadros, 18 September 2017. Philippines: 1 male (17.4 × 14.9 mm), 1 female (14.9 × 12.7 mm) [photographed] (ZRC 2022.0973), stn M52, Danao embayment, Panglao Island, coll. Panglao Marine Biodiversity Project, 30 June 2004.— 1 female (15.9 × 13.4 mm) (ZRC 2022.0974), Kawasan, Cebu, coll. H.-C. Liu, 25 November 2001. Vietnam: 1 male [photographed] (17.4 × 15.2 mm) (ZRC 2022.0975), stn CD-I-08 (22), Bay Canh Island, 08°40.125’N 106°40.933’E, coll. 14 April 2010.— 1 female [photographed] (14.1 × 12.0 mm) (ZRC 2022.0976), stn CD-I-08 (24), Bay Canh Island, 08°40.125’N 106°40.933’E, coll. 14 April 2010.— 1 male [photographed] (16.0 × 13.5 mm) (ZRC 2022.0977), stn CD-I-08 (23), Bay Canh Island, 08°40.125’N 106°40.933’E, coll. 14 April 2010.— 8 males (16.5 × 14.2 mm, 14.0 × 12.0 mm, 7.6 × 6.3 mm, 6.1 × 5.1 mm), 17 females (16.2 × 13.1 mm, 14.9 × 12.6 mm, 7.6 × 6.5 mm, 5.0 × 4.3 mm) (ZRC 2022.0978), stn CD-I-08, Bay Canh Island, 08°40.125’N 106°40.933’E, coll. 14 April 2010. Malaysia: 1 male (14.0 × 11.8 mm) (ZRC 2022.0979), Sungei Baharu mangrove, Pulau Tioman, coll. LSM4263 students, 18 July 2014.— 1 male (11.6 × 9.8 mm) (ZRC 2016.0140), Telok Bakau, Pulau Tulai, Pulau Tioman, Pahang, coll. H.H. Tan & M.A.H. Chua, 16 July 2016.— 1 male (12.8 × 11.0 mm) (ZRC 2022.0980), Sungei Baharu mangrove, Pulau Tioman, coll. B.Y. Lee, 15 July 2014.— 2 males (12.5 × 11.0 mm, 8.2 × 7.8 m) (ZRC 2022.0981), Sungei Baharu mangrove, Pulau Tioman, coll. B.Y. Lee, 15 July 2014.— 1 female (17.6 × 14.6 mm) (ZRC 2000.1655), Pulau Manukan, Kota Kinabalu, Sabah, coll. C.D. Schubart, 22 June 2000.— 2 females (12.8 × 10.5 mm, 9.0 × 7.7 mm), 1 ovigerous female (12.5 × 10.1 mm), 1 juvenile female (5.5 × 4.9 mm) (ZRC 1969.10.13.3), Johore Straits, coll. C.L. Soh, 5 October 1969.— 3 males (12.8 × 11.0 mm, 9.8 × 8.8 mm, 9.7 × 8.6 mm), 4 females (15.8 × 13.8 mm, 13.4 × 11.3 mm, 9.3 × 8.0 mm, 7.7 × 6.6 mm) (ZRC 2022.0982), near Sungei Lengara, Langkawi Island, coll. A.D. Tran et al., 20 November 2006.— 2 males (12.5 × 11.0 mm, 9.6 × 8.3 mm) (ZRC 2022.0983), river mouth of Sungei Temurun, Langkawi, coll. T. Naruse, 20 November 2006.— 10 males (13.3 × 11.4 mm, 13.2 × 11.0 mm, 8.7 × 7.3 mm, 7.4 × 6.6 mm), 3 females (11.5 × 9.7 mm, 6.7 × 5.7 mm, 6.7 × 5.5 mm) (ZRC 1969.10.14.1–10), Johore Straits, coll. C.L. Soh, 12 October 1969. Indonesia: 1 male (11.2 × 9.7 mm), near NAD resort, Mawali Bay, Pulau Lembeh, Manado, Sulawesi, coll. H.H. Tan, December 2018. Diagnosis. Carapace slightly wider than long,almost square; postfrontal lobes weak, divided by weak longitudinal grooves; median pair slightly prominent, nearly equal in proportions. Inner orbital angle present, rounded, distinct, slight gap between inner orbital angle and frontal margin (Fig. 7C). Anterolateral margin of carapace with distinct external orbital angle, second tooth blunt, weak or absent; posterolateral margin slightly convex (Figs. 2B, C, 7A). Chelipeds dorsal surface of dactylus of chela with between 20–31 evenly spaced tubercles, proximal tubercles small, increasing in size medially, decreasing in size distally (Fig. 5E); presence of single longitudinal pectinated ridge with between 28–45 chitinous comb-like tubercles on dorsal surface of chela; row of 10–20 granules clustered behind pectinated ridge on chela; inner surface of palm granulated, vertical rows of 6–10 granules in adult male (Fig. 5F). P5 merus relatively short, wide, length approximately 0.36–0.43 times width (Fig. 6E–K). G1 slightly curved, distal region slightly wide; chitinous tip narrow, short; tip with dense tufts of setae, single row of plumose setae on exterior lateral margin; chitinous tip visible when denuded (Fig. 11A–D). Female vulvae with central operculum, round, slightly protruded (Fig. 8D). Description. Carapace slightly wider than long, almost square; covered with dense coat of setae, including small tufts of setae resembling tubercles; carapace margin fringed with dense, short setae; carapace smooth when denuded. Postfrontal lobes weak, divided by weak longitudinal grooves; median pair slightly prominent, nearly equal in proportions. Inner orbital angle present, rounded, distinct, slight gap between inner orbital angle and frontal margin (Fig. 7C). Anterolateral margin of carapace with distinct external orbital angle, second tooth blunt, weak or absent; posterolateral margin slightly convex (Figs. 2B, C, 7A). Antenna short. Antennules folding transversely. Third maxilliped with merus relatively rounded. Epistomial margin relatively narrow (Fig. 7C). Chelipeds subequal in size; large, robust in 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 between 20–31 evenly spaced tubercles, proximal tubercles small, increasing in size medially, decreasing in size distally (Fig. 5E); absent or weak granules in female and juveniles; presence of single longitudinal pectinated ridge with between 28–45 chitinous comb-like tubercles on dorsal surface of chela; row of 10–20 granules clustered behind pectinated ridge on chela; inner surface of palm granulated, vertical rows of 6–10 granules in adult male (Fig. 5F). P2–P5 covered with dense coat of setae, with small tufts of setae resembling tubercles, longer setae on dorsal and ventral margins except distal portion of dactylus (Figs. 2B, C, 7A); P5 merus relatively short, wide, length approximately 0.36–0.43 times width (Fig. 6E–K). Male thoracic sternum sparsely covered with short setae, smooth when denuded; sternites 1 and 2 fused, with suture between fused sternites 3 and 4; sternopleonal cavity extends nearly to edge of sternites 1 and 2. Male pleon wide and stout, long setae fringed pleon margin; somite 3 widest; somite 6 with curved edge; telson wide, dome-shaped (Fig. 7B); male pleonal locking mechanism absent, without tubercle on sternite 5. G1 slightly curved, distal region slightly wide; chitinous tip narrow, short; tip with dense tufts of setae, single row of plumose setae on exterior lateral margin; chitinous tip visible when denuded (Fig. 11A–D). G2 shorter than G1, slightly curved, tip rounded. Female pleon rounded, relatively wider than long; telson dome-shaped (Fig. 8C). Vulvae with central operculum, round, slightly protruded; sternal vulvar cover slightly raised above operculum (Fig. 8D). Colouration. Chelipeds with fingers yellowish white and purple to purplish red palm (Fig. 2B, C). In life, entire crab covered in a thin layer of mud. Etymology. The term, “ nobile ” alludes to the distinctive colour of the chela of the species; purple being a colour normally associated with royalty. Remarks. Clistocoeloma nobile n. sp. has a mix of diagnostic characters of C. villosum and C. suvaense. In the form of the carapace, C. nobile n. sp. has a weak external orbital angle on the anterolateral margin of carapace (Figs. 2B, C, 7A), and this is intermediate in form between C. villosum (which has no external orbital angle visible; Fig. 1A) and C. suvaense (which has a distinct external orbital angle; Figs. 2A, 3A, 4A). This character is very consistent in the large series of specimens of C. nobile n. sp. examined. With regards to the armature on the dorsal margin of the dactylus of the male chela, C. nobile n. sp. has 20–31 granules (Fig. 5E), in contrast to only16 granules present in C. villosum (Fig. 5A). The number of granules in C. suvaense (22–27; Figs. 3E, 5C), however, overlaps with that of C. nobile n. sp. The G1of C. suvaense is also very similar to that of C. nobile n. sp., with the lateral view appearing stout with a distinct angle before chitinous tip in C. suvaense (Figs. 9F, 10B, F) while the lateral view appearing narrower with a weak angle visibile before the chitinous tip in C. nobile n. sp. (Fig. 11B). The lateral view of the G1 of C. villosum, on the other hand, appears narrow with no clear angle before chitinous tip (Fig 9B). In addition, C. nobile n. sp. can also be separated from C. suvaense in having a rounded and slightly protruded vulvar cover (Fig. 8D); which is ovate and less protruded vulvar cover in C. suvaense (Fig. 8B). Females of C. villosum s. str. are not known. On the basis of these characters, it is clear that most of the records of “ C. villosum ” from the IWP, including Singapore, belong to C. nobile n. sp. instead. For the record by Tesch (1917: 208–210, pl. 17 fig. 2), his description and figures of the female specimen match C. nobile n. sp.. Tesch (1917) had noted that the New Guinea specimens has a distinct external orbital angle, in contrast to the type of C. villosum described by De Man (1987: 644) which has an indistinct one. The older records of “ Cleistocoeloma suvaense ” from Singapore by Tan & Ng (1994) and Wee & Ng (1994), are based on specimen records in the ZRC, are here referred to C. nobile n. sp. instead. A number of records of “ C. villosum ” from the IWP, however, are in doubt as we have neither specimens from these areas nor good descriptions and/or figures on which to base our decisions (see later). Ecological notes. Clistocoeloma nobile n. sp. is not a mangal species, although it has been found in habitats near mangroves. Most of the Singapore specimens were found in muddy substrates amongst the rocky intertidal areas in the supralittoral zone, typically found under large rocks with muddy substrate. For the Japanese specimens (as C. villosum), it was observed by Komai et al. (2004) that it can be found underneath rocks or fallen leaves within the landward side of the mangrove, while Yuhara et al. (2017) noted that this species was found underneath gravels and cobble stones around the edges of mangrove forests. For the Korean material, Lee et al. (2010) noted that the species occurred in “slightly moist soil under fallen leaves”. Distribution. Singapore (type locality), Sumatra (De Man 1897, 1898), Caroline Islands (Rathbun 1907), New Guinea (Tesch 1917), the Philippines (McNeill 1968), Taiwan (Li 2015; Li et al. 2019), Japan (Komai et al. 2004; Yuhara et al. 2017; Takakura & Komai 2019), and South Korea (Lee et al. 2010).Published as part of 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), pp. 217-236 in Zootaxa 5318 (2) on pages 226-234, DOI: 10.11646/zootaxa.5318.2.3, http://zenodo.org/record/816248