Labuanium vitatum, Ng, Peter K. L. & Davie, Peter J. F., 2011

Ng, Peter K. L. & Davie, Peter J. F., 2011, Labuanium vitatum (Crustacea: Decapoda: Brachyura: Sesarmidae), a new Indo-West Pacific species of arboreal crab, Zootaxa 2889, pp. 35-48 : 37-43

Labuanium vitatum new species

( Figs. 1 , 2 A, 3A, 4A, 5A, B, 6A, 7, 8, 10A–G)

Sesarma oceanicum — Alcock 1900: 423; George 1978: 14 [not Sesarma oceanica De Man, 1889 = Labuanium rotundatum ( Hess, 1865) ]

Sesarma (Episesarma) rotundata papuo -malesiaca— Nobili 1900: 510 (part). [not Sesarma (Episesarma) rotundata papuo - malesiaca Nobili, 1899]

Sesarma (Sesarma) rotundata — Tesch 1917: 193 (in part).

Labuanium rotundatum — Serène & Soh 1970: 401 (part); Hicks et al. 1984: 64; Davie, 2002: 221 (part); Ng & Liu 2003: 614 (part); Ng et al. 2008: 221 (in part).

Material examined. Holotype male (34.8 × 34.9 mm) ( WAM C 13977 ), 60 m above beach, on tree trunk, on track to West White Beach, Christmas I., coll. D. Merton, 11 February 1978. Paratypes: 1 male (39.5 × 38.5 mm) ( WAM C257-89), The Dales, Christmas I., coll. H. Yorkston, ca. January 1989; 1 female (35.2 × 33.6 mm) ( WAM C258- 89), Greta Beach, Christmas I., coll. H. Yorkston, 23 December 1988. Others: 1 male (22.3 × 21.8 mm) ( RMNH 1202), Tjibodas, Java, Indonesia, coll. J. Boerlarge, 1888; 1 male (25.5 × 24.9 mm) ( RMNH 1989), Nias, Indonesia, coll. E. E. W. G. Schröder, 1908; 1 male (34.5 × 33.1 mm) ( ZRC 2009.0099), Cuthbert Bay, Andaman Is., coll. P. Biswas, 2001.

4. Right third maxillipeds of Labuanium species. A, L. vitatum new, holotype male (34.8 × 34.9 mm) ( WAM C 13977 ), Christmas I.; B, L. papuomalesiacum ( Nobili, 1899) , male (38.0 × 37.4 mm) ( SMF 1971.18.5.53), Caroline Is.; C, L. scandens Ng & Liu, 2003 , male (29.6 × 28.7 mm) ( ZRC 2002.478), Taiwan.

Diagnosis. Carapace width and length subequal; antero-dorsal surfaces finely granular, posterior surfaces almost smooth ( Fig. 2 A); posterolateral regions with fine granular oblique striae ( Fig. 2 A); postfrontal cristae prominent, sharp, medially separated by deep cleft ( Figs. 2 A, 3A); merus of third maxilliped in adult male longitudinally ovate, ca. twice as long as broad (Fig. 4A); inner margin of cheliped carpus with prominent triangular tooth, margins distinctly serrated in large males ( Fig. 5 A); outer surface of chela with numerous small, closely arranged rounded granules ( Figs. 5 A, B; 7A, B); dorsal margin of small male chela, with a non-pectinated ridge on outer edge of about 44 small granules, with 2 shorter, less distinct oblique rows of granules posterior to it ( Fig. 5 B), in large males, ridges indistinct ( Fig. 7 B) to almost indiscernible ( Fig. 5 A), with granules appearing relatively larger, more scattered; dorsal surface of cheliped dactylus with row of distinct granules, about 12 in smaller males ( Fig. 5 B), 10 or 11 in larger males ( Figs. 5 A, 7B); outer surface of ambulatory meri weakly rugose, dorsal margin finely granulated ( Figs. 2 A, 7C, D); male abdominal somite 6 broader than long, distal part of lateral margins convex, proximal part slightly sinuous ( Fig. 6 A); abdominal telson as long as somite 6, subtriangular in shape with rounded tip ( Fig. 6 A); G1 relatively stout; distal part bent about 45° from vertical, distal chitinous part relatively short, beak-like, subtruncate ( Fig. 10 A–D).

Etymology. The name is Latin meaning for “shun” and “frustrating to find.” It alludes to the naturally secretive habits of the species.

Remarks. This species was first recorded from Christmas I. by George (1978) under the name of Sesarma oceanica De Man, 1889 (his specimen is here designated as the holotype of Labuanium vitatum new species). Sesarma oceanica is still considered a subjective junior synonym of Labuanium rotundatum ( Hess, 1865) .

Labuanium vitatum new species is superficially similar to L. papuomalesiacum but they can be easily separated by their G1 morphology. In L. papuomalesiacum , the G1 is relatively longer and the pectinated distal part is proportionately longer and almost straight ( Fig. 10 H, I) whereas in L. vitatum new species, the G1 is proportionately shorter and the pectinated distal part is shorter and gently sinuous ( Fig. 10 A, B). The lateral carapace margin of larger adult L. papuomalesiacum is also relatively more convex ( Figs. 2 B, 9) (relatively straighter in similarly sized L. vitatum new species, Figs. 2 A, 8), the merus of the third maxilliped is relatively shorter (Fig. 4B) (relatively longer in L. vitatum new species, Fig. 4A), and the dorsomarginal ridge of granules on the chela of L. papuomalesiacum is distinct in adult males ( Fig. 5 C) (diffuse and poorly demarcated in large L. vitatum new species, Figs. 5 A, 7B). These differences also apply for L. scandens ( Fig. 2 C).

Variation. The second anterolateral tooth of the paratype female is more prominent than in the males. The inner angle of the cheliped carpus also has a distinct large triangular tooth which is dorso-ventrally flattened and appears almost lobiform; whereas in males, it is less prominent and the margins appear almost serrated ( Fig. 5 A). The gastric regions of the males are also slightly more swollen. The two relatively small specimens from Nias (RMNH 1989) and Java (RMNH 1202) ( Fig. 8 A, B) resemble the types from Christmas I. except that the granules lining the outer marginal ridge on the chela are distinct ( Fig. 5 B); and the lateral margins of the G1 are relatively more sinuous ( Fig. 10 F, G). We also tentatively refer one male from Andaman Is. (ZRC 2009.0099) to this species although it is peculiar in having a relatively smoother dorsal carapace surface, lower anterolateral teeth and proportionately longer ambulatory propodi ( Fig. 8 C). Its G1 structure, however, agrees very well with the holotype male of L. vitatum new species. Because this male specimen is not fully hardened (it had moulted shortly before it was preserved) and both its chelae are missing, it nevertheless seems best to refer it to L. vitatum new species, for the moment.

Colour. The colour appears to be somewhat variable. An adult male (paratype, 39.5 × 38.5 mm, WAM C257- 89) was a uniform yellowish brown overall ( Fig. 1 C) while a smaller female (paratype, 35.2 × 33.6 mm, WAM C258-89) was more brightly coloured, with a purplish carapace with beige lateral margins, with the legs pale purple, and the palm bright purple with red fingers ( Fig. 1 A, B). The eyes are bright greenish-yellow in both specimens. The holotype male (34.8 × 34.9 mm, WAM C 13977 ) was described on the label as “Deep brownish-purplish on carapace and legs. Hands purplish with vertical (narrow) white stripe between bases of pollex and dactylus on both inner and outer surfaces of hand”. Hicks et al. (1984: 64) notes that it is known as the “White-stripe crab” in Christmas I. because of the beige lateral carapace margins.

Notes on habits. Like most of its congeners, Labuanium vitatum new species is an arboreal species, and has been collected usually at the base of trees in relatively close proximity to the sea (although one specimen was obtained on a vegetated limestone platform at 60 m altitude). Hicks et al. (1984: 64) notes that individuals grow up to 40 mm in carapace width and spawn about the time of the full moon between November and April. The chief warden on Christmas I., Max Orchard, has spent many years on the island and despite a strong personal interest in crabs, has seen this species only once on the night of 15 April 2010 at Andersons Dale, and he noted “… I was walking back up along the stream in pouring rain and edging around a tree when I caught a glimpse of a crab with bright yellow eyes and brownish carapace on a tree about 1.5 metres above the ground” (M. Orchard, personal communication). As with L. rotundatum from Guam and L. scandens from Taiwan, they are apparently mostly active mainly in wet weather and at night ( Ng & Liu 2003).

Distribution. Christmas I. ( Hicks et al. 1984); Nicobar Is. ( Alcock 1900), Nias ( Nobili 1899, 1900), west Java ( Tesch 1917).

Comparative material. In addition to the specimens listed in Ng & Liu (2003) for L. rotundatum sensu lato and L. scandens , the following new material was examined: Labuanium scandens Ng & Liu, 2003 — 1 male (29.6 × 28.7 mm), 1 female ( ZRC 2002.478), Hsiang Chiao Wan, Kentin National Park, southern Taiwan, coll. P. K. L. Ng & C. H. Wang, 5 August 2002. Labuanium rotundatum — 2 males (24.0 × 24.2 mm, 26.5 × 27.5 mm), 2 females (24.7 × 24.7 mm; 17.9 × 17.8 mm) (syntypes of Sesarma gardineri Borradaile, 1900 ) (Cambridge University Zoology Museum), Ellice Is., Funafuti, Tuvalu, coll. J. S. Gardiner, 1897.

Figures

FIGURE 1. Colours in life of Labuanium vitatum new species. A, B, female (35.2 × 33.6 mm) (WAM C 258 - 89), Greta Beach, Christmas I (courtesy Hugh Yorkston).; C, male (39.5 × 38.5 mm) (WAM C 257 - 89), The Dales, Christmas I (courtesy Peter Greenaway).

FIGURE 2. Overall views of Labuanium species. A, L. vitatum new species, holotype male (34.8 × 34.9 mm) (WAM C 13977), Christmas I.; B, L. papuomalesiacum (Nobili, 1899), male (38.0 × 37.4 mm) (SMF 1971.18.5.53), Caroline Is.; C, L. scandens Ng & Liu, 2003, holotype male (42.3 × 41.2 mm) (TMCD 3290), Taiwan.

FIGURE 5. Dorsal views of major male chelae of Labuanium species. A, L. vitatum new species, holotype male (34.8 × 34.9 mm) (WAM C 13977), Christmas I.; B, L. vitatum new species, male (25.5 × 24.9 mm) (RMNH 1989), Nias; C, L. papuomalesiacum (Nobili, 1899), male (38.0 × 37.4 mm) (SMF 1971.18.5.53), Caroline Is.; D, L. scandens Ng & Liu, 2003, male (29.6 × 28.7 mm) (ZRC 2002.478), Taiwan.

FIGURE 6. Thoracic sternal views and abdomens of Labuanium species. A, L. vitatum new species, holotype male (34.8 × 34.9 mm) (WAM C 13977), Christmas I.; B, L. papuomalesiacum (Nobili, 1899), male (38.0 × 37.4 mm) (SMF 1971.18.5.53), Caroline Is.; C, L. scandens Ng & Liu, 2003, holotype male (42.3 × 41.2 mm) (TMCD 3290), Taiwan.

FIGURE 7. Labuanium vitatum new species, holotype male (34.8 × 34.9 mm) (WAM C 13977), Christmas I .. A, outer view of left chela; B, fourth right ambulatory leg; C, third right ambulatory leg.

FIGURE 8. Overall views of Labuanium vitatum new species. A, male (22.3 × 21.8 mm) (RMNH 1202), Java; B, male (25.5 × 24.9 mm) (RMNH 1989), Nias; C, male (34.5 × 33.1 mm) (ZRC 2009.0099), Andaman Is.

FIGURE 10. Denuded gonopods of Labuanium species. A – E, L. vitatum new species, holotype male (34.8 × 34.9 mm) (WAM C 13977), Christmas I.; F, G, L. vitatum new species, male (22.3 × 21.8 mm) (RMNH 1202), Java; H – K, L. papuomalesiacum (Nobili, 1899), male (38.0 × 37.4 mm) (SMF 1971.18.5.53), Caroline Is. A, B, C, D, F, G, left G 1; H, I, J, K, right G 1, E, left G 2. Scales: A, B, E, F, G, H, I = 1.0 mm; C, D, J, K = 0.5 mm.