Clistocoeloma melanesicum, Lee, B. Y., Ng, N. K. & Ng, L., 2013

Lee, B. Y., Ng, N. K. & Ng, L., 2013, On the identity of Clistocoeloma balansae A. Milne-Edwards, 1873, and C. tectum (Rathbun, 1914), with description of a new species from the West Pacific (Crustacea: Decapoda: Sesarmidae), Zootaxa 3641 (4), pp. 420-432 : 428-431

Clistocoeloma melanesicum n. sp.

( Figs. 7–9 )

Material examined. Holotype: male (14.2 × 12.8 mm) (MNHN-IU-2012-995), station VM34, intertidal, Palikulo Peninsula, Vanuatu (15º29.4’S, 167º15.2’E), coll. SANTO 2006, 23 September 2006.— Paratypes: 1 male (11.4 × 10.2 mm) (ZRC 2012.706), Vanuatu, Espiritu Santo, coll. P. K. L. Ng et al., 11 September 2006.— 1 female (13.0 × 11.4 mm) (MNHN-IU-2012-996), station VM4, intertidal, between Rose point and Nasouli River, Vanuatu (15º34.9’S, 167º01.8’E), coll. SANTO 2006, 11 September 2006.— 1 male (12.2 × 10.9 mm), 1 female (15.3 × 13.5 mm) (USNM), station VM34, intertidal, Palikulo Peninsula, Vanuatu (15º29.4’S, 167º15.2’E), coll. SANTO 2006, 23 September 2006.— 2 males (14.2 × 12.6 mm, 12.0 × 10.8 mm), 1 female (14.5 × 13.0 mm) (ZRC 2012.708), Station VM34, intertidal, Palikulo Peninsula, Vanuatu (15º29.4’S, 167º15.2’E), coll. SANTO 2006, 23 September 2006.—Additional material: 1 female (13.7 × 12.1 mm) (QM W24229), Le Cap, West coast, New Caledonia, no other data.—2 damaged males (14.5 × 12.6 mm, 16.3 × 14.1 mm), 1 damaged female (13.7 × 12.1 mm) (QM W27351), Tararo mangrove forest, southeast central Isabel I., Solomon Islands, no other data.

Type locality. Vanuatu.

Description. Carapace slightly wider than long, almost square, covered with dense coat of setae, among which stands small tufts of setae resembling tubercles; denuded carapace with smooth surface ( Fig. 7 A). Postfrontal lobes distinct, divided by longitudinal grooves; distal pair indistinct ( Fig. 7 A). Inner orbital angle present, pronounced ( Fig. 7 C). Carapace dorsal-ventrally flattened. Regions less defined.

Anterolateral margin of carapace with 3 triangular teeth, inclusive of external orbital angle ( Fig. 7 A): Anterolateral teeth well defined by setae on margin; second and third tooth less distinct when denuded; posterolateral margin slightly convex. Entire margin of carapace fringed with dense, short setae.

Chelipeds equal or subequal in size; large, robust in males; small, slender in female. Outer surface of chela smooth when denuded. Dorsal surface of carpus covered with small tufts of setae resembling tubercles, smooth when denuded. Single longitudinal pectinated ridge present on dorsal surface of chela, with about 37 fine teeth; dorsal surface of movable dactylus of chela with 19 or 20 tubercles, evenly spaced, proximal tubercles small, increasing in size medially, decreasing in size distally ( Fig. 8 ). Tubercles on movable dactylus of chela present in female but smaller, less distinct. Inner surface of palm of adult male granular, with single vertical row of approximately 6 granules, widely spaced ( Fig. 8 B). Row of tubercles present behind pectinated ridge on inner surface of male chela ( Figs. 8 A, 8C).

Walking legs covered with dense coat of setae, with small tufts of setae resembling tubercles, smooth when denuded; longer setae on dorsal and ventral margins of entire leg except dactylus; meri with a deep groove subdistally. Third walking leg: merus approximately 2 times longer than wide; combined length of carpus and propodus almost similar to length of merus; propodus approximately 2.7 times longer than wide.

Thoracic sternum setose, covered with short setae. Abdomen of male wide; widest at somite 3; telson oval shape ( Fig. 7 B). Long setae fringed margins of abdomen. Female abdomen wider, round, telson half embedded in sixth abdominal somite. Tip of G1 with dense tufts of setae, single row of setae on exterior margin; chitinous tip visible when denuded ( Fig. 9 B–D).

Etymology. This species is named after the geographical region of which Vanuatu, Solomon Islands, and New Caledonia are part of, the geographical distribution of the new species.

Remarks. Clistocoeloma melanesicum n. sp. is superficially similar to C. balansae in carapace features, especially before the setae are removed. Once denuded, the differences are apparent—the dorsal carapace surface of C. melanesicum n. sp. being smooth with the postfrontal lobe indistinctly separated by short and shallow longitudinal grooves ( Fig. 7 A) (granular carapace surface and the postfrontal lobe distinctly divided into two by deep grooves in C. balansae ; Figs. 1 A, 2A, 3A); and the second and third anterolateral teeth are relatively low ( Fig. 7 A) (pronounced in C. balansae , Figs. 1 A, 2A, 3A). Whereas the male chela has a row of granules on the inner surface of the chelae in both species, that of C. melanesicum n. sp. has fewer number of granules (six), which are more widely spaced (fig. 8B) compared to C. balansae ( Fig. 4 B), which has more granules (nine) that are more closely spaced. The pectinated ridge on both species has different granule counts, with C. melanesicum n. sp. having more than C. balansae (37 versus 30). There is also a row of granules behind the pectinated ridge on the male chela of C. melanesicum n. sp. ( Fig. 8 B), whereas only a single granule can be seen behind the pectinated ridge on the male chela ( Fig. 4 B) of C. balansae . The overall male abdomen shapes for both species are similar, but it is usually relatively narrower in C. melanesicum n. sp. ( Fig. 7 B vs. Fig. 3 B). The overall structure of the G1 of C. melanesicum n. sp. is relatively narrower and less stout ( Fig. 9 ) than in C. balansae , in contrast to a G1 that is proportionately wider subdistally in C. balansae ( Fig. 5 ).

Distribution. New Caledonia, Vanuatu, and, Solomon Islands.

Ecological notes. It is noteworthy that both C. balansae and C. melanesicum n. sp. are present in New Caledonia and Vanuatu. While we do not have detailed ecological data for New Caledonia, the specimens of C. balansae and C. melanesicum n. sp. were mostly collected from different types of mangrove forests; however, the respective mangrove species were not identified. Clistocoeloma balansae appears to inhabit coastal patch mangroves next to the open sea in Vanuatu, whereas C. melanesicum n. sp. was found in denser mangrove forests near rivers. Only one specimen of C. melanesicum n. sp. was collected together with C. balansae at the fringe mangroves between Rose Point and Nasouli River.

Figures

FIGURE 1. Clistocoeloma balansae A. Milne-Edwards, 1873, lectotype male (20.7 × 19.7 mm) (MNHN B 10912), New Caledonia. A, dorsal overall view; B, ventral view of abdomen and thoracic sternum; C, frontal view of carapace. (Photographs by T. Naruse)

FIGURE 3. Clistocoeloma balansae A. Milne-Edwards, 1873. A – C, male (15.9 × 15.5 mm) (ZRC 2012.702), Philippines; D, female (17.2 × 16.9 mm) (ZRC 2012.702), Philippines. A, dorsal overall view; B, ventral view of abdomen and thoracic sternum; C, D posterior view of carapace.

FIGURE 4. Clistocoeloma balansae A. Milne-Edwards, 1873, male (15.9 × 15.5 mm) (ZRC 2012.702), Philippines. A, outer view of left chela; B, inner view of left chela; C, dorsal marginal view of left chela.

FIGURE 5. Clistocoeloma balansae A. Milne-Edwards, 1873, male (15.9 × 15.5 mm) (ZRC 2012.702), Philippines. A, male abdomen; B, G 1 dorsal view; C, G 1 lateral view; D, G 1 ventral view. G 1 denuded.

FIGURE 7. Clistocoeloma melanesicum n. sp. Holotype male (14.2 × 12.8 mm) (MNHN-IU- 2012 - 995), Vanuatu: A, dorsal overall view; B, ventral view of abdomen and thoracic sternum; C, frontal view of carapace; D, posterior view of carapace.

FIGURE 8. Clistocoeloma melanesicum n. sp. Holotype male (14.2 × 12.8 mm) (MNHN-IU- 2012 - 995), Vanuatu. A, outer view of left chela; B, inner view of left chela; C, dorsal marginal view of left chela.

FIGURE 9. Clistocoeloma melanesicum n. sp. Holotype male (14.2 × 12.8 mm) (MNHN-IU- 2012 - 995), Vanuatu. A, male abdomen; B, G 1 dorsal view; C, G 1 lateral view; D, G 1 ventral view. G 1 denuded.