Nautilothelphusa Balss, 1933

Ng, Oliver K. S. Chia Peter K. L., 2006, The Freshwater Crabs Of Sulawesi, With Descriptions Of Two New Genera And Four New Species (Crustacea: Decapoda: Brachyura: Parathelphusidae), Raffles Bulletin of Zoology 54 (2), pp. 381-428 : 412

Nautilothelphusa Balss, 1933

[ Parathelphusa ] ( Nautilothelphusa ) Balss, 1933: 94. Para-Nautilo-thelphusa - Balss, 1934: 179.

Nautilothelphusa - Balss, 1937: 144; Bott, 1969: 366; 1970c: 132.

Diagnosis. – Carapace squarish, rugose. Frontal margin with distinct, well developed median triangle, deeply recessed. Anterolateral margin with 2 epibranchial teeth; external orbital angle larger, extends beyond frontal margin, all teeth acutely triangular. Posterior margin of epistome with distinctly triangular median lobe. Third maxilliped exopod with long flagellum extending beyond width of merus. Chelipeds equal even in large adult males, fingers very slender, with both pollex and dactylus longer than palm. Last pair of ambulatory leg with very broad (dorsoventrally flattened) propodus. Male abdomen distinctly T-shaped, narrow, with proximal segments broader but narrowing sharply from segments 5 onwards. G1 stout, simple, terminal and subterminal segments indistinctly or cannot be demarcated, terminal segment truncate; G2 shorter than G1, basal segment longer than well developed distal segment.

Remarks. – This genus was established by Balss (1933) (as a subgenus) for an unusual new species he described from “ Java ” (actually Sulawesi, see later) - [ Parathelphusa ] (Nautilothelphusa) zimmeri . Its squarish carapace shape, peculiar lateral carapace armature, flattened last pair of ambulatory propodi and very short stout G1 with a flared tip are disgnostic features. Bott (1970c) recognized the genus but expanded its definition to include Parathelphusa matannensis (here referred to its own new genus, Syntripsa ). Ng (1988), in a brief commentary on the genus Parathelphusa and related genera, noted that the inclusion of P. matannensis in Nautilothelphusa was not coherent and transferred it back to Parathelphusa . In the process, he also did not recognize Bott’s (1970c) Palawanthelphusa as a valid genus and lso synonymised it with Parathelphusa (see also Ng & Goh, 1987).

The features of Nautilothelphusa are unusual in that it suggests the species is more natatorial than Parathelphusa and Syntripsa species. The carapace shape and dorsoventrally flattened last pair of ambulatory propodi, reminiscent of those in swimming crabs of the family Portunidae suggests this. However, the specis has yet to be observed actually swimming. The legs, however, have been seen to used to help them burrow backwards into the sand. The long slender chelae (in both sexes) suggests that their food is different, perhaps being more dependent on worms or small fish. Certainly, they are not the more massive structures seen in adult Parathelphusa and Syntripsa which can be usd to crush the many mollusks in the lakes. In its ambulatory legs, Nautilothelphusa is very similar to Migmathelphusa , although the distance between and different origins of Lake Poso and the Malili Lakes suggests the similarities may be due to convergent evolution, and perhaps a product of living in lakes.