Platythelphusa polita Capart, 1952

Reed, Sadie K. & Cumberlidge, Neil, 2006, Brachyura: Potamoidea: Potamonautidae, Platythelphusidae, Deckeniidae (), Zootaxa 1262 (1), pp. 1-139 : 1-139

23. Platythelphusa polita Capart, 1952 (Fig. 195, plate XXIII)

Platythelphusa polita Capart, 1952: 455–57 , figs. 7d, e, g; Cumberlidge, 1999: 277; Cumberlidge et al., 1999: 1507–1509, fig. 5, 7h, i, 8e, o, p, 9e, 10p–s; Marijnissen et al., 2004: 528–530, Tables 1, 2.

Potamonautes (Platythelphusa) polita — Coulter, 1991: 253–255, tables 9.XX, 9.XXI.

Type material examined: Lake Tanganyika , paratypes, adult female, ovigerous (cw 13 mm), adult male (cw 14 mm) ( BMNH 1952.10.23.34–35) .

Additional material: TANZANIA: See Cumberlidge et al. (1999).

Diagnosis. Carapace sub­hexagonal, rounded, medium wide (cw/fw 2.4), slightly wider than long (cl/fw 2.1), high (ch/fw 1.1). Front deflexed slightly, edge smooth, each external corner marked by small, low tooth. Exorbital angle produced into broad low tooth, epibranchial tooth very small. Three teeth on anterolateral margin (small epibranchial tooth anteriormost, other two teeth large, subequal, directed forward). Sidewalls of carapace divided by epimeral sulcus into two parts, faint vertical sulcus can be detected under close examination. Suborbital margin lined by small granules, small tooth at medial end. Margins of inferior surface of merus of cheliped smooth; single large pointed distal tooth on medial inferior margin; superior margin of merus of p1 with short carinae. Inner margin of carpus of cheliped with two large subequal medial teeth, articular tooth (at point of articulation with propodus) low, blunt; outer margin of carpus smooth. Merus of p5 shorter than fw, distal tooth on superior margin of p2–p5 low. Propodus of p4 slim with smooth margins, propodus of p5 short, broad, margins of propodi of p5 flat, widened, smooth. Dactylus of p5 very short, only half as long as dactylus of p4. Dactyli of p2–p5 slim, curved, with rows of long spines. Terminal article of gonopod 1 directed sharply outward at 80° angle to the vertical, stout, cone­shaped, tapering to pointed tip.

Description. See Capart (1952) and Cumberlidge et al. (1999).

Size. The adult size range is from cw 12 to cw 18 mm.

Distribution. Lake Tanganyika: Burundi, Tanzania and D. R. Congo. Platythelphusa polita occurs in waters from 5–60 m deep, where the lake bottom is either sandy or rocky and there are shell beds. This species is sometimes found inside empty Neothauma shells.

Remarks. This species was redescribed by Cumberlidge et al. (1999), who provided details of its identification, distribution and ecology. The terminal article of gonopod 1 is directed outward at an 80° angle to the vertical, rather than at a 60° angle, as stated in Cumberlidge et al. (1999). Platythelphusa polita is morphologically close to P. maculata but differs in the form of the articular tooth of the carpus of p1 (which is a sharp spine in P. maculata and a low, blunt tooth in P. polita ), by the carapace height (which is medium high in P. polita and flat in P. maculata ) and by the size of the epibranchial tooth (which is extremely small in P. polita and large and pointed in P. maculata ). There are clear differences between P. polita and P. armata . These include the body size at maturity (cw 12 to cw 13 mm in P. polita and cw 35 to cw 37 mm in P.armata ), the articular tooth of the carpus of p1 (low and blunt in P. polita and sharp and pointed in P. armata ) and the terminal article of gonopod 1 (angled at 80° to the vertical in P. polita and at 90° to the vertical in P. armata ). Platythelphusa polita is distinguished from juvenile P. armata by the relatively high carapace, by the dimorphism of the male chelipeds, by fewer spines on the anterolateral margin of the carapace and by the distinctly smaller epibranchial tooth of P. polita . Differences between P. polita and P. echinata include the carapace height (medium height in P. polita and very flat in P. echinata ), the inferior margins of p2–p5 (smooth in P. polita , very spiny in P. echinata ), the margin of the merus of p1 (smooth in P. polita , very spiny in P. echinata ), the frontal margin (smooth in P. polita , very spiny in P. echinata ) and the suborbital margin (smooth in P. polita , very spiny in P. echinata ).

Natural history and conservation status. The conservation status of P. polita is categorized as least concern (LC) ( Table 4) because it has a range of occurrence and an area of occupancy in excess of the thresholds for vulnerable (VU) ( IUCN 2004). Its population is estimated to be stable based on indirect measures such as the fact that a material has been collected recently from more than one locality (R. Bills, pers comm.).