Neosarmatium bidentatum, 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 : 578-583

Neosarmatium bidentatum n. sp. ( Figs 3 ; 4 )

TYPE MATERIAL. — Indonesia. Holotype: Ajkwa , Papua, 22.X.2001, ♂ 20.0 × 18.0 mm ( QM).

Paratype: Minajerwi, Papua, 5.VIII.1999, ♂ 22.5 × 19.2 mm ( MZB Cru 1539).

ETYMOLOGY. — Neuter form of the Latin dentatus, meaning tooth, in reference to the characteristic pair of teeth on the dorsal surface of the dactylus of the male cheliped.

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.

DISTRIBUTION. — So far only known from the type locality on the south-west coast of Papua, Indonesia.

DESCRIPTION

Carapace ( Fig. 3A, B ) transversely subrectangular, 1.1 times broader than long, distinctly vaulted, entire surface minutely punctate, glabrous, shiny, but with well spaced, short tufts of setae over anterior half; posteriorly setae in rows along branchial ridges; gastric region well defined, cardiac region indistinct. Four distinct posterolateral branchial ridges; first curving inward from margin of second anterolateral tooth and reaching point inline with middle of orbit; second slightly longer, arising inside lateral margin; third about same length as first but not quite reaching lateral margin; fourth arising from lateral margin, sinuous, ending over coxa of last leg. Lateral margin sinuous; posterior margin straight. Front 0.5 times carapace width, moderately deflexed, with broad median concavity. Postfrontal lobes swollen, separated by deep narrow grooves; lateral lobes narrow, half width of medians. Exorbital angle acutely triangular; anterolateral margin with two blunt teeth behind exorbital angle; first tooth deeply incised, with lateral margin about twice length of exorbital tooth, without ridges on inner surface; second tooth much smaller but still distinct. Upper orbital border weakly convex, oblique, finely granular over outer half. Lower orbital border evenly, finely granular. Eyes not extending beyond exorbital tooth. Antennal and antennular basal segments adjacent, not separated by septum; basal antennular segment swollen. Antennal flagellum relatively long, almost reaching lower orbital margin; with very fine terminal setae, as long again as flagellum. Third maxillipeds ( Fig. 4C ) relatively slender; ischium with shallow, longitudinal, median sulcus; merus with distinct oblique, setose, submedian ridge ending near mesial margin; exopod slender, reaching to half length of outer margin of merus, flagellum long; inner margins of merus and ischium lined with long dense setae, proximal outer margin of ischium and base of exopod with dense setae.

Chelipeds ( Figs 3E ; 4B ) equal, robust. Merus with posterior border minutely granular, without subdistal spine; inner and outer anterior borders more coarsely granular, otherwise unarmed; outer face with fine granular striations, anterior face smooth, inner face with longitudinal row of setae. Carpus with inner angle slightly produced, armed with a few blunt granules; inner margin unarmed, a tuft of long setae proximally on secondary ventral ridge of inner margin; a row of several larger tubercles on inner face of carpus below inner angle; outer surface with sparse striations. Palm with outer surface naked, coarsely punctate; strongly raised rounded crest extending from just above articulation of dactyl almost to superior posterior margin ( Fig. 3F ); a low, barely discernible medial longitudinal ridge; row of short setae on margin of gape below dactyl articulation; inner surface of palm mostly smooth, punctate, with raised tuberculate crest arising behind dactylar articulation and continuing as rounded granules onto fixed finger for about half length. 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. 3D ) with two inwardly directed, chitinousspine tipped teeth on inner-side of proximal quarter; distal-most tooth placed dorsal to large subproximal tooth on cutting margin; first tooth placed halfway towards base of dactyl; otherwise dactyl smooth and rounded. Both fingers with chitinous tips; wide gape between cutting margins.

Second and third pairs of walking legs subequal, longer than others, about 1.7 times maximum carapace width. Merus of third leg 2.3 times as long as wide; anterior margin of merus with an acute subdistal spine. Meri of legs 1-3 each with faint short, transverse striae on upper surface, and sparse, small, sharp granules; merus of fourth leg smooth. Carpi of legs 1-3 each with two low ridges on outer surface, lower ridge more distinct, dorsal half with distinct covering of short setae, and small tufts of longer setae, but not completely hiding surface. Propodi similarly covered with setae on dorsal twothirds. Carpus of third leg 2.1 times as long as wide; propodus of third leg 2.2 times longer than wide. Dactylus 0.9 times length of propodus, slightly recurved, evenly tapering, 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. 4D ) moderately broad; telson evenly rounded, length 0.63 times sixth segment; sixth segment 1.1 times longer than wide, lateral margins slightly convex; segments 3-5 progressively tapering, 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 almost straight in ventral view, apical section abruptly narrowed, set obliquely, tip corneous. Male second gonopod very short.

REMARKS

As mentioned under N. papuense n. sp., N. bidentatum n. sp. belongs to the group of species that have very deep bodies, sinuous lateral margins with antero- and posterolateral margins distinct, and well developed, strong chitinous teeth on the dorsal surface of the dactyl of the male chela. In this group, only N. indicum , N. malabaricum and N. punctatum have two dorsal chitinous teeth as in N. bidentatum n. sp. Neosarmatium indicum also has a diagnostic protruding basal shelf on the outer face of the fixed finger, below the gape of the male chela, and also a different positioning of the dorsal dactylar teeth, with one dactylar tooth placed medially, and the other subproximally. Both N. malabaricum and N. punctatum differ from N. bidentatum n. sp. in having the inner surface of the cheliped palm with a strongly raised, protruding, granular, vertical crest. In N. bidentatum n. sp., however, the crest is low, not markedly enlarged or prominent, and consists of some enlarged granules. Neosarmatium malabaricum and N. punctatum also differ from N. bidentatum n. sp. in the positioning and size of the dactylar teeth. Neosarmatium bidentatum n. sp. shares in common with N. malabaricum and several other Neosarmatium species the presence of a strong longitudinal rim marking the outer edge of the upper surface of the palm of the cheliped.

Neosarmatium bidentatum n. sp. is also similar in general appearance to N. daviei and N. papuense n. sp. It differs from the latter two in having only two instead of three dorsal dactylar teeth differently positioned; by having a more elongate sixth male abdominal segment; by having a strong longitudinal rim marking the outer edge of the upper surface of the palm of the cheliped; and by having a longer lateral margin on the first anterolateral carapace tooth. Neosarmatium bidentatum n. sp. differs conspicuously from N. papuense n. sp. by having a strong, deeply incised first anterolateral carapace tooth. The male first gonopods of each species are also obviously different. In particular, the distal part of the male first gonopod of N. bidentatum n. sp. is relatively longer than that of N. daviei , but conversely also not as slender as that of N. papuense n. sp.

KEY TO THE INDO- WEST PACIFIC SPECIES OF NEOSARMATIUM SERÈNE & SOH, 1970 (modified from Davie 1994, and Schubart & Ng 2002) This key relies heavily on characters from male chelae. However, the female chelae usually show the same features, albeit less obvious, and thus is also useful in identification.

1. Lateral carapace margins more or less straight, without clear antero- and posterolateral separation ................................................................................................................... 2

— Lateral carapace margins more or less sinuous, antero- and posterolateral margins relatively clearly demarcated ...................................................................................................... 3

2. Carapace rectangular, lateral margins weakly convergent posteriorly; anterolateral margin with a distinct tooth behind exorbital angle; dorsal margin of cheliped dactylus with 4 evenly spaced tubercles; chelipeds subequal ..................................................... N. laeve

— Carapace trapezoidal, lateral margins strongly convergent posteriorly; anterolateral margin without a tooth; dorsal margin of cheliped dactylus with 4 large submedian tubercles and row of numerous small granules along proximal margin; chelipeds distincly unequal .... ........................................................................................................................ N. tangi

3. Anterolateral margin entire, or if a low angular tooth behind exorbital angle then not separated by a deep notch from rest of margin (exorbital breadth subequal to length of carapace; male unknown) ................................ N. integrum (A. Milne-Edwards, 1873)

— Side of carapace with 1 or 2 anterolateral teeth (second often reduced to angular projection) ........................................................................................................................... 4

4. Dactyl of male cheliped with strong chitinous teeth on dorsal margin ........................ 5

— Dactyl of male cheliped either without strong chitinous teeth on dorsal margin, or bearing small, sharp, chitinous spinules only ................................................................... 13

5. Dactyl of male cheliped with 2 teeth on dorsal margin ............................................... 6

— Dactyl of male cheliped with 3-5 teeth on dorsal margin ............................................ 9

6. Male chela with protruding basal shelf on outer face of fixed finger below gape; 1 dactylar tooth placed medially, the other subproximally .......................................... N. indicum

— Male chela without protruding basal shelf on outer face of fixed finger below gape .... 7

7. Inner surface of palm without strongly raised, granular, vertical crest (4 or 5 granules may be prominent on large males but are not raised onto a protruding crest); dorsal dactylar tubercles restricted to proximal quarter; distal-most tooth placed dorsal to large subproximal tooth on cutting margin; first tooth placed halfway towards base of dactyl ............. ..................................................................................................... N. bidentatum n. sp.

— Inner surface of palm with a strongly raised, granular, vertical crest; dactylar tubercles otherwise positioned .................................................................................................. 8

8. Distal tooth on upper surface of dactyl placed close to middle; upper surface of palm of cheliped with strong longitudinal rim marking outer edge; carapace 1.15-1.25 times longer than wide ................................................................................. N. malabaricum

— Distal tooth on upper surface of dactyl placed clearly less than half-way to tip; longitudinal rim present on upper surface of palm of cheliped but not strongly differentiated; carapace 1.25-1.35 times longer than wide ............................................................ N. punctatum

9. Dactyl of male cheliped with 3 tubercles (one may be smaller and non-chitinous) on dorsal margin ........................................................................................................... 10

— Dactyl of male cheliped with 4 or 5 teeth on dorsal margin .................. N. rotundifrons

10. Carapace distinctly vaulted, more or less rectangular (1.2-1.28 times wider than long); carapace dorsal surface almost smooth, setae present as very short, small tufts, hardly discernible; sixth segment of male abdomen not markedly elongated (much wider at base than long) ................................................................................................................ 11

— Carapace squarish (less than 1.2 times wider than long); carapace dorsal surface with prominent tufts and rows of setae; sixth segment of male abdomen markedly elongated (length equal to width) ............................................................................................. 12

11. First anterolateral carapace tooth sharply angular, prominent, anteriorly directed, separated from exorbital angle by a deep V-shaped notch; dorsal surface of dactyl typically with 3 chitinous teeth on proximal half ..................................................................... N. daviei

— First anterolateral carapace tooth low, blunt, separated from exorbital angle by broad U-shaped sulcus; dorsal surface of dactyl bearing 3 teeth on proximal third, a pair of closely-set chitinous teeth, and 1 very small, proximal, non-chitinous tooth ............... N. papuense n. sp.

12. Dactylar teeth truncate, spaced evenly over proximal half .............................. N. smithi

— Dactylar teeth acute, set close together over proximal two-fifths ............ N. trispinosum

13. Dactyl of cheliped smooth, unarmed (walking legs relatively slender, length of merus of third walking leg 2.6-2.7 times width; male first gonopod short, with distal portion not strongly narrowing, and not much twisted) .............................................................. 14

— Dactyl of cheliped armed with small, sharp, chitinous spinules ................................ 15

14. Inner angle of carpus of cheliped unarmed; inner face of palm with vertical row of granules behind gape .................................................................................................. N. inerme

— Inner angle of carpus of cheliped armed with acute granular projection; inner face of palm with a patch of granules ventrally but not extending as a vertical row behind gape ........ ............................................................................................................... N. spinicarpus

15. Carapace with second anterolateral tooth weakly marked; male chela c. 1.7 times longer than high; lower margin evenly convex; dactylar spinules evenly spaced in a single row, and extending only to about half or two-thirds length of dactyl; vertical granular row on inside of chela strongly developed .............................................................. N. meinerti

— Carapace without indication of a second anterolateral tooth; male chela c. 1.8 times longer than high; lower margin straight behind fixed finger; dactylar spinules more numerous, not confined to a single row, and extending almost to tip of dactyl; vertical granular row on inside of chela relatively lower .......................................................... N. fourmanoiri

Dedication

We dedicate this paper to Patsy A. McLaughlin, a major figure in crustacean research, but also a friend and mentor.

Figures

FIG. 3. — Neosarmatium bidentatum n. sp., holotype ♂ 20.0 × 18.0 mm, Indonesia (QM): A, dorsal view; B, carapace; C, frontal view; D, dorsal dactylar tubercles of cheliped; E, frontal view of chela; F, dorsal view of top of palm showing low granular crest on inner face.

FIG. 4. — Neosarmatium bidentatum n. sp., paratype ♂ 20.0 × 18.0 mm,Indonesia (QM):A, carapace antero-lateral region;B, left cheliped; C, left third maxilliped (setae removed);D, abdomen;E-H, male left first gonopod (setae removed); E, F, ventral view;G, H, lateral view. Scale bars: A, B, D, 5 mm; C, E, G, 1 mm; F, H, 0.5 mm.