Neosarmatium papuense, Rahayu & Davie, 2006

Rahayu, Dwi Listyo & Davie, Peter J. F., 2006, Two new species of mangrove crabs of the genus Neosarmatium Serène & Soh, 1970 (Decapoda, Brachyura, Sesarmidae) from Papua, Indonesia, Zoosystema 28 (2), pp. 573-584 : 574-578

Neosarmatium papuense n. sp.

( Figs 1 ; 2)

TYPE MATERIAL. — Indonesia. Holotype: Kamora , Papua, 19.IV.2004, ♂ 16.6 × 13.3 mm ( MZB Cru 1538).

Paratypes: Ajkwa , Papua, 15.V.2001, ♂ 15.5 × 13.0 mm ( ZRC) ; Ajkwa , Papua, 16.IV.2004, 2 ♂♂ 13.2 × 11.2, 12.5 × 9.8 mm ( QM, MNHN) .

ETYMOLOGY. — Named after the Indonesian region where it has so far only been found.

HABITAT. — Burrows in firm, moist mud in mangrove forest. Present specimens were all collected from a zone about 500 m landward from the river bank. This new species sometimes co-occurs with Sarmatium germaini (A. Milne-Edwards, 1869) .

DISTRIBUTION. — So far known only from the west coast of Papua, Indonesia.

DESCRIPTION

Carapace ( Fig. 1A, B ) transversely rectangular, c. 1.2 times broader than long, distinctly vaulted, entire surface minutely punctate; gastric region well defined, cardiac region indistinct. Branchial ridges prominent; first relatively short, beginning on posterior edge of first anterolateral tooth; second relatively long, arising from last anterolateral tooth; third arising from or just short of lateral margin; fourth arising from lateral margin. Lateral margin weakly sinuous, subparallel along most of length before curving to join straight posterior margin. Front ( Fig. 1C ) 0.4 times carapace width, slightly deflexed, margin with slight median concavity. Lateral postfrontal lobes narrow, not as swollen as medians; median lobes separated by narrow groove. Exorbital angle triangular. Anterolateral margin with one forwardly directed tooth behind exorbital angle, blunt, larger than exorbital angle; second anterolateral tooth minute, barely discernible. Setae in short tufts on anterior half, and posteriorly in rows along branchial ridges; carapace surface otherwise glabrous and shiny. Upper orbital border weakly convex, finely granular.Lower orbital border evenly, finely granular. Eyes extending slightly beyond edge of exorbital tooth. Antennal and antennular basal segments adjacent, not separated by septum; basal antennular segment swollen. Antennal flagellum relatively long, entering orbit. Ischium of third maxilliped ( Fig. 2C) with shallow, longitudinal, median sulcus; merus with distinct oblique, setose, submedian ridge ending near mesial margin; exopod slender, tip reaching to half length of outer margin of merus, flagellum long. Inner margin of merus and ischium with setae, proximal outer margin of ischium and base of exopod with dense setae.

Chelipeds ( Figs 1E ; 2B) subequal, robust. Merus with posterior border minutely tuberculate, without subdistal spine; outer anterior border serrated, ending in blunt subdistal spine; inner anterior border with tubercles; outer surface with fine striations, inner surface with longitudinal row of setae. Carpus with inner angle slightly produced, armed with a few blunt tubercles; inner margin unarmed, a tuft of long setae proximally on secondary ventral ridge of inner margin; a few granules present on inner face of carpus just below inner angle; outer surface with sparse striations.Palm with outer surface naked; low, barely discernible medial longitudinal ridge; row of short setae in gape below articulation with dactyl; inner surface of palm mostly smooth, with strongly raised granular vertical crest, continuing obliquely for about one-third of fixed finger. Fixed finger smooth, slightly flattened on outer surface; moderately long. Length of cutting edge 0.5 times length of propodus. Cutting margins of fixed finger and dactyl with larger rounded teeth subproximally and subdistally, with even row of very small teeth between. Dorsal surface of dactyl ( Fig. 1D ) with low elevation over proximal one-third, bearing two chitinous teeth and one small non-chitinous proximal tooth; short setae at base. Fingers with chitinous tips, wide gape between cutting margins.

Second pair of walking legs longer than others, about 1.4 times maximum carapace width.Merus of third leg 2.2 times as long as wide; anterior margin of merus with an acute subdistal spine. Meri of legs 1-3 each with faint transverse striae on upper surface, merus of fourth leg smooth. Carpi of legs 1-3 each with two ridges on outer surface, dorsal half with mat of short setae. Propodi each with dorsal two-thirds covered by mat of short setae. Carpus of third leg 1.7 times as long as wide; propodus of third leg twice as long as wide. Dactyls 0.95 length of propodi, terminating acutely, two rows of short setae on outer surface.

Thoracic sternites 1-3 fused; surface scarcely setose. Sternites 3 and 4 separated by low ridge obscured by dense setae. Abdominal cavity reaching just below low ridge separating sternites 3 and 4.

Male abdomen ( Fig. 2D) moderately wide; telson evenly rounded, as long as preceding segment; sixth segment 1.5 times wider than long, lateral margins slightly convex; segments 3-5 progressively more trapezoidal, lateral margins of segment 4 and 5 straight; lateral margins of third segment strongly convex; first and second segments similar in width to third segment, but longitudinally very narrow. Male first gonopod ( Fig. 2 E-H) almost straight in ventral view, outer margin weakly concave. Male second gonopod very short.

REMARKS

The form and position of the dorsal dactylar teeth on the cheliped are very important characters for separating most Neosarmatium species. In N. papuense n. sp., the dorsal surface of the dactyl has a low elevation over the proximal third with two prominent, upwardly directed, chitinous teeth, and a small non-chitinous proximal tooth. Also, on the carapace the second anterolateral tooth is barely discernible or just a trace in the smallest specimen.

Neosarmatium papuense n. sp. and N. bidentatum n. sp. belong to a group of species that have very deep bodies, sinuous lateral margins with the antero- and posterolateral margins distinctly demarcated, and well developed, strong chitinous teeth on the dorsal surface of the dactyl of the male chela. The other members of this group are: N. indicum , N. integrum , N. malabaricum (Henderson, 1893) , N. punctatum (A. Milne-Edwards, 1873) , N. rotundifrons , N. daviei , N. smithi (H. Milne Edwards, 1853) and N. trispinosum . All species in this group can be distinguished using the new key

B

A presented here. Neosesartium papuense n. sp. differs from N. indicum , N. malabaricum , N. punctatum and N. bidentatus n. sp., primarily in having two chitinous teeth and one smaller non-chitinous tooth on the dorsal surface of the cheliped dactyl. Other differences between N. papuense n. sp. and N. bidentatus are discussed under the latter new species.

In N. papuense n. sp. and N. trispinosum , the three teeth on the dorsal margin of the dactyl of the cheliped are set closely together subproximally, but the shape is different. In N. trispinosum , all teeth are large, acute and more spine-like, while in N. papuense n. sp. two teeth are distinctly blunt, and one proximal-most tooth is smaller. Specimens of N. trispinosum and N. papuense n. sp. of similar size have been compared, and the characteristic dorsal dactylar armature appears consistent with size-related variations. Even though the available specimens of N. papuense n. sp. are small, they are likely close to their adult size as they show the robust, strong condition of spines typical of adult Neosarmatium crabs. Also, N. trispinosum and its closest sister-species N. smithi (see Davie 1994) share a significantly elongated sixth segment of the male abdomen, that is quite different in appearance to the proportionately shorter one of N. papuense n. sp. This character is also consistent for equivalent sized specimens of N. trispinosum .

Figures

FIG. 1. — Neosarmatium papuense n. sp., paratype ♂ 15.5 × 13.0 mm, Indonesia (ZRC): A, dorsal view; B, carapace; C, frontal view; D, dorsal dactylar tubercles of cheliped; E, frontal view of chela; F, ventral view.