Sundathelphusa, 2008

Schubart, Christoph D. & Ng, Peter K. L., 2008, A new molluscivore crab from Lake Poso confirms multiple colonization of ancient lakes in Sulawesi by freshwater crabs (Decapoda: Brachyura), Zoological Journal of the Linnean Society 154 (2), pp. 211-221 : 214-218

publication ID 10.1111/j.1096-3642.2008.00441.x


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( FIG. 1–4 View Figure 1 View Figure 2 View Figure 3 View Figure 4 )

Holotype – male (24.6 by 20.4 mm) ( MZB 1480 View Materials ), under rocks, c. 2 m depth, Lake Poso , west coast, near Taipa, Sulawesi, Indonesia, coll. C.D. Schubart, T.M. Leong & D. Wowor, 22 January 2000.

Paratypes – eight males (smallest 11.7 by 10.2 mm, largest 23.5 by 20.4 mm), eight females (smallest 12.0 by 10.0 mm, largest 24.7 by 20.3 mm), two juveniles ( ZRC 2000.1703 View Materials ), two males, two females ( MZB 1481 View Materials ), same data as holotype .

Diagnosis: Dorsal surface of carapace convex, relatively smooth, not prominently inflated or swollen. Frontal medium triangle complete, margins completely fused. External orbital angle broadly triangular; anterolateral margin distinctly convex, with one distinct tooth. Adult chelipeds markedly heterochelous in both sexes; major chela with strong molariform teeth at the bases of the cutting edges of fingers. Male abdomen distinctly T-shaped: segment 6 longer than telson. First gonopods gently curving outwards; terminal segment c. 0.3 times the total length.

Description of holotype: Carapace appears quadrate, widest point of carapace about one-third of the distance from front, carapace gently convex transversely; regions poorly demarcated, relatively smooth; cervical groove distinct, broad; H-shaped gastrocardiac groove distinct; shallow transverse depression between cardiac and intestinal regions. Frontal median triangle complete, lateral and dorsal margins cristate, dorsal and lateral margins fused, but suture still visible. Epigastric cristae: low, rounded, but still discernible, separated from each other by shallow cleft. Postorbital cristae: very low, rugose, almost indiscernible. Frontal margin truncate, about half the maximum carapace width, appears vaguely bilobed from dorsal view; supraorbital margin entire, subparallel with frontal margin. External orbital tooth broadly triangular, clearly directed anteriorly, outer margin uneven, straight, twice as long as inner margin, separated from anterolateral margin by distinct V-shaped cleft, tip not extending beyond level of front. Anterolateral margin distinctly convex, slightly granular, and gently curving to join posterolateral margin. Posterolateral margin gently convex, converging gradually towards more concave posterior carapace margin. Suborbital, sub-branchial, and pterygostomial regions covered with scattered oblique short striae and small granules. Basal antennal segment large, subquadrate. Posterior margin of epistome with large median triangular lobe; lateral margins sinuous. Third maxilliped with ischium rectangular, submedian oblique sulcus distinct; merus subquadrate, with gentle median depression, anteroexternal angle rounded; tip of exopod reaching to midpoint of outer margin of merus, flagellum long.

Chelipeds prominently unequal. Merus with slightly serrated margins, no distinct subdistal tooth. Carpus with outer surface rugose, with welldeveloped inner distal spine that is somewhat laterally flattened, and proximal basal part with several small sharp tubercles. Outer surface of minor palm gently rugose to almost smooth; fingers longer than palm, cutting edges lined with numerous teeth and denticles, tip pectinated. Outer surface of major palm smooth or finely punctate; fingers subequal to length of palm, proximal two-thirds of cutting edge of pollex with large molariform tooth, rest of edge with distinct teeth; proximal one-fifth of cutting edge of dactylus with relatively smaller molariform tooth, rest of edge with numerous teeth and denticles, slender, tip pectinated.

Ambulatory legs not elongate, second leg longest. Merus with dorsal, slightly serrate margin, subdistal angle with low tooth but no spine. Carpus elongate, dorsal margin gently serrated, ventral margin smooth, and outer surface with two low ridges. Dorsal and ventral margins of propodus serrated. Dactylus slender, slightly flattened laterally, gently curved.

First to fifth thoracic sternites smooth, with scattered punctae; all sternites fused, no sutures evident. Abdominal cavity reaching to imaginary line joining anterior edge of coxae of chelipeds. Male abdomen distinctly T-shaped. Segment 1 very narrow longitudinally, proximal and distal margins gently sinuous. Segment 2 subrectangular transversely. Segments 3–5 gradually more trapezoidal; lateral margins of segment 3 convex; lateral margins of segments 4 and 5, straight to gently concave. Segment 6 longitudinally rectangular, longer than telson, and lateral margins gently sinuous. Telson longitudinally triangular, lateral margins concave, and tip rounded.

First gonopods gently curving outwards; subterminal segment with outer margin gently concave; terminal segment c. 0.3 times total gonopod length, slightly curved, subcylindrical, tip gently rounded. Second gonopods elongated, much longer than first; distal segment long, c. 0.7 times the length of the basal segment.

Paratypes: The paratype males agree with the holotype male in all major aspects, although in smaller specimens, the major chela is relatively smaller. The carapaces of smaller specimens also tend to be more quadrate. Females agree with the males in most non-sexual characters, although the lateral margins in larger specimens are slightly more convex, giving them a somewhat more inflated appearance. The heterochely in females is also less prominent, with the major claw being much smaller than in males of equivalent sizes, but still showing molariform dentation.

Colour in life: Pale yellow; carapace darker, somewhat olive; legs lighter; chelae homogeneously yellow, except shining white molariform teeth.

Etymology: The name ‘molluscivora’ (mollusc-eating) is used as an adjective, and is derived from the taxon name ‘Mollusca’ and the Latin verb ‘vorare’ (to devour). It makes reference to the apparent mollusceating habit of these crabs, as suggested by their chelar morphology.

Distribution: This species has only been found from its type locality in Lake Poso (Sulawesi, Indonesia), to which it is probably endemic.

Remarks: The genus Sundathelphusa Bott, 1969 (type species Potamon (Geothelphusa) cassiope De Man, 1902 , by original designation) currently contains 28 species from the Philippines, Sulawesi, Moluccas and eastern Borneo ( Ng & Stuebing, 1989; Ng, 1991; Ng & Sket, 1996; Takeda & Ng, 2001). The genus is dominant in the Philippines, with only three species known from Sulawesi thus far, viz. Sundathelphusa cassiope ( De Man, 1902) , Sundathelphusa minahassae ( Schenkel, 1902) , and Sundathelphusa rubra ( Schenkel, 1902) .

The authors have examined photographs of the whole type specimens, with figures of the G1s and G2s of S. cassiope , S. minahassae , and S. rubra that were prepared for us by Oliver Chia (National University of Singapore) at our request (see also Chia & Ng, 2006). As such, we have no doubt that our present specimens from Poso belong to a new species. The most obvious character that distinguishes adults of S. molluscivora sp. nov. from all congeners is the large molariform tooth on the larger chela. Such a character is present in only two other freshwater crabs of the region, viz. Syntripsa matannensis ( Schenkel, 1902) and Syntripsa flavichela Chia & Ng, 2006 , both from the Malili lake system in central Sulawesi.

The carapaces of S. cassiope and S. rubra are both prominently swollen, with the dorsal surface strongly convex and the branchial regions swollen. In addition, their G1 terminal segments are proportionately much shorter. The same is true of Potamon (Geothelphusa) angustipes Schenkel, 1902 , a species that was tentatively synonymized with S. rubra by Bott (1970: 74) (see also Schenkel, 1902: 533, pl. 11 fig. 17; Chia & Ng, 2006). In the form of the flat carapace and the structure of the G1, S. molluscivora sp. nov. is morphologically closest to S. minahassae . However, S. molluscivora sp. nov. can easily be separated, in that its anterolateral margin is more strongly convex, and the posterolateral regions are smoother, with very low transverse striae.

Two other species of Sundathelphusa are known from near Sulawesi in the Moluccas, viz. Sundathelphusa aruana ( Roux, 1911) and Sundathelphusa halmaherensis ( De Man, 1902) . Sundathelphusa molluscivora sp. nov. differs from S. aruana in its prominently flatter carapace, with the latter resembling S. cassiope in carapace physiognomy (cf. types examined, see also Bott, 1970: 75, 76; Chia & Ng, 2006: figs 42, 43). The status of S. halmaherensis is not clear, as it is only known from juveniles, but it is a species with a clearly more rugose carapace (see De Man, 1902: 561, pl. 20, fig. 17; Bott, 1970: 78, pl. 14, figs 67–69; Cai & Ng, 2001: 686), and is not conspecific with the much smoother S. molluscivora sp. nov.

The molecular phylogeny places the new species S. molluscivora sp. nov. next to an unidentified species of the genus, with high confidence values. This sister species was found in a small stream draining into Lake Poso, but could not be identified to species level, because only one juvenile individual was available, and thereby lacked diagnostic morphological characters. Also, the third representative of Sundathelphusa in this study, S. minahassae , belongs to this clade. Sundathelphusa minahassae was collected in the northeastern part of Sulawesi, and the very long branches document pronounced genetic differences between the two species from the central highlands.

The three species of Sundathelphusa as a group are reciprocally monophyletic to all the other species of freshwater crabs from Sulawesi belonging to the genera Syntripsa, Migmathelphsua , Parathelphusa , and Nautilothelphusa . Within this latter group, the genus Syntripsa from the Malili Lakes holds the most basal position. The next split separates tributaries and the lake from the Poso system from the tributaries and lakes from the Malili system, giving the overall speciation pattern a clear hydrogeographic component. The genera Syntripsa , Migmathelphusa , and Nautilothelphusa exclusively comprise lake crabs, demonstrating from their phylogenetic position that the lakes must have been colonized several times independently.