Platythelphusa immaculata Marijnissen, Schram, Cumberlidge & Michel, 2004

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

21. Platythelphusa immaculata Marijnissen, Schram, Cumberlidge & Michel, 2004

(Fig. 193, plate XXI)

Platythelphusa immaculata Marijnissen et al., 2004: 515–525 , Fig. 1A–D, Tables 1, 2.

Type material examined: TANZANIA: Lake Tanganyika , Cape Mpimbwe near Katondo Point, (7°05.59’S, 30°30.00’E), male holotype (cw 18.2 mm), 7 m depth, sand and rocks, (G. Kazumbe), 9.ii.2003 ( ZMA De. 204594) .

Additional material examined: TANZANIA: Lake Tanganyika , Mzungu Point (4°55.05’S, 29°35.73’E), adult female paratype (cw 25.7 mm) 0 m depth, cobbles and sand (S. Marijnissen pers. comm.) 23.ix.2002 ( ZMA De.204599) .

Diagnosis. Carapace subhexagonal, rounded, wider than long (cw/fw 2.7, cl/fw 2.2), very flat (ch/fw 0.9). Anterior margin of front granular, with square angles produced into sharp, pointed teeth. Exorbital tooth broad, directed forward. Anterolateral margin between exorbital and epibranchial teeth granulate. Epibranchial tooth broad, pointed; two large teeth on anterolateral margin behind epibranchial tooth. Suborbital margin tuberculate, with narrow, pointed tooth at medial end. Lateral superior and inferior margins of merus of cheliped granular. Inner margin of carpus of cheliped with two large subequal carpal teeth, articular tooth (at point of articulation with propodus) broad, pointed; outer margin of carpus either granulate or with several small teeth. Cheliped manus concave, propodus and dactylus with spatula­like tips. Marked sexual dimorphism in cheliped shape; males with enlarged major cheliped, propodus and dactylus with molar dentition; propodus and dactylus of minor cheliped with serrated dentition; females with almost monomorphic chelae, lined with serrated dentition. Merus of p5 almost as long as fw. Subdistal tooth on superior margin of merus p2–p4 a small spine, distal tooth either a small spine or small and low. Inferior margin propodus of p2–p4 smooth. Dactyli of p3–p4 with row of minute spines on superior margin and several larger distal spines; inferior margin smooth, with several distal spines. Terminal article of first gonopod directed sharply outward at 90° angle to vertical; slim, cone­shaped, tapering strongly to pointed tip.

Color. Dorsal carapace of living specimens grey­pink to orange­brown, without stains or spots, and the tips of the chelipeds and pereiopods are white.

Distribution. The species is known only from Lake Tanganyika, in the vicinity of Kigoma, Tanzania.

Remarks. Specimens were collected from underneath rocks and cobbles at depths ranging from 2 to 20 meters. Platythelphusa immaculata is sympatric with P. conculcata , P. echinata and juveniles of P. armata . Platythelphusa immaculata is morphologically close to P. denticulata , but the two taxa can be distinguished by the carapace height, which is flattened in P. immaculata and high in P. denticulata ( Marijnissen et al. 2004) .

Natural history and conservation status. The conservation status of P. immaculata is categorized as near threatened (NT) ( Table 4) in view of its narrow distribution and low area of occupancy, together with the fact that it is known from a relatively few specimens (S. Marijnissen, pers comm.) ( IUCN 2004).