Platythelphusa armata A. Milne­Edwards, 1887

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

17. Platythelphusa armata A. Milne­Edwards, 1887 (Fig. 189, plate XVII)

Potamonautes (Platythelphusa) armata armata — Bott, 1955: 226–227, pl. 2, fig. 1a–d, 9a–b; Coulter, 1991: 253–255, tables 9.XX, 9.XXI, fig. 2, 3.

Platythelphusa armata — Cumberlidge, 1997: 584; 1998: 208; 1999: figs. 8A,C, 9A, 10A, 11A,AA, 12 A,F, 13, A,AA; Cumberlidge et al., 1999: 1493–1498, figs. 1, 7a–b, 8a,g–h, 9a, 10a–d; Marijnissen et al., 2004: 528–530, Tables 1, 2.

Type material: Lake Tanganyika , female type (cw 64.5, cl 52.7 mm) (M. Joubert) ( MNHN) .

Additional material examined: TANZANIA: Lake Tanganyika , 2 males (W. A. Cunnington) ( USNM 39470 ) .

Diagnosis. Carapace subhexagonal, rounded, medium height (ch/fw 1.07). Frontal margin granulated, with large forward pointing tooth at each external corner. Epibranchial tooth large, pointed. Three teeth (two large and one smaller) on anterolateral margin behind epibranchial tooth. Suborbital margin lined by small pointed teeth, distinct spine at medial end. Margins of inferior surface of merus of cheliped both smooth or only faintly granulated, single large pointed distal tooth at distal end of medial inferior margin; superior margin of merus of p1 with rows of prominent, rough grains, short carinae. Inner margin of carpus of cheliped with two long slender pointed teeth (second as long as first); long, pointed articular tooth on carpus where it contacts propodus; outer margin of carpus with small granules. Merus of p5 longer than fw, distal tooth of superior margin low, blunt. Propodus of p4 long, thin; propodus of p5 short, broad; margins of propodi of p5 widened, smooth. Terminal article of gonopod 1 directed outward at a 45° angle to vertical; coneshaped, tapering to pointed, upward­directed tip. Adult size range from cw 35 to cw 47.5 mm.

Distribution. Platythelphusa armata is endemic to Lake Tanganyika, and has been recorded from the waters of all four countries bordering the lake ( Tanzania, Burundi, Zambia and D. R. Congo). This is the largest and most distinctive species in the genus and is mainly found in rocky areas, at depths between 5– 30 m. The juveniles are found in the sublittoral shell zone from 1–10 m deep in places where the lake bed is rocky, or in the empty shells of Neothauma sp. where they co­ occur together with the adults of small­bodied species such as P. maculata , P. echinata and P. polita ( Coulter 1991; Cumberlidge et al. 1999). The juveniles of P. armata are often found inside the empty shells of the gastropod Neothauma tanganyicense .

Remarks. This species was recently redescribed by Cumberlidge et al. (1999), who provided details of the identification, distribution and ecology of this species. The angle of the terminal article of gonopod 1 is revised here as being directed outward at a 45° angle to the vertical (rather than at a 90° angle as stated in Cumberlidge et al. 1999).

Natural history and conservation status. The conservation status of P.armata is categorized as least concern (LC) ( Table 4) because it has a range of occurrence and an area of occupancy well 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 lot of material has been collected recently from more than one locality (S. Marijnissen, pers. comm.), that this species is the subject of a local commercial fishery with large numbers captured regularly and that it is well represented in museum collections.