Potamonautes semilunaris Bott, 1955

Meyer, Kirstin S. & Cumberlidge, Neil, 2011, A revision of the freshwater crabs (Crustacea: Decapoda: Brachyura: Potamonautidae) of the Lake Kivu drainage basin in Central and East Africa, Zootaxa 3011, pp. 45-58 : 54

Potamonautes semilunaris Bott, 1955

( Fig. 9–11 , Table 1 , 2)

Potamonautes (Rotundopotamonautes) emini semilunaris— Bott 1955: 291, fig. 43; plate 24, fig. 2a–d. Potamonautes semilunaris— Ng et al. 2008: 171; Cumberlidge et al. 2009: appendix item 954.

Type material examined. DR CONGO: Terifwazi, southwest of Mount Kahuzi, near Lake Kivu, adult male lectotype (CW 20.0, CL 13.7, CH 6.7, FW 5.2), adult male (CW 21.0, CL 14.7, CH 7.0, FW 5.0), adult male (CW 17.9, CL 13.0, CH 6.6, FW 4.3), adult female (CW 19.5, CL 14.4, CH 7.5, FW 4.8), juvenile (CW 12.4, CL 9.3, CH 4.9, FW 3.0) (R. Laurent) ( SMF 2429).

Diagnosis. Carapace medium height ( CH /FW 1.3), surface smooth, postfrontal crest incomplete, epigastric crests not meeting postorbital crests, latter crests granulated laterally; exorbital, epibranchial teeth absent; horizontal sulcus on carapace sidewall lacking granules; ischium of third maxilliped with faint vertical sulcus; sternal sulcus s2/s3 deep; s3/s4 present at sides, missing in middle, not meeting top of sac; first carpal tooth on carpus of cheliped distinct, pointed; second carpal tooth small, pointed; distal meral tooth of P1 merus distinct, pointed; fixed finger of propodus lined by small, rounded teeth, with two prominent ones in proximal region; dactylus of major cheliped slender, fingers enclosing oval interspace, dactylus lined by small, rounded teeth, with prominent one about a third of the way along dactylus; terminal article of G1 slim, strongly curved outward, crescent shaped; lateral, medial folds low, even; groove on terminal article not visible on dorsal face; dorsal membrane broad, margins of equal width ( Fig. 9 , 10 ).

Size. A small species with an adult size range of CW 21–22 mm.

Type locality. DR Congo, Terifwazi, southwest of Mount Kahuzi, near Lake Kivu ( Fig. 11 ).

Conservation status. Potamonautes semilunaris was listed as “data deficient” ( IUCN 2003; Cumberlidge et al. 2009). This species is known from only two localities in the DR Congo, but further information on its range, ecological requirements, population size, population trends, and long-term threats is lacking ( Cumberlidge 2008d).

Distribution. DR Congo, Bunyakiri and Terifwazi, adjacent to Lake Kivu ( Fig. 11 ; Table 2).

Remarks. Potamonautes semilunaris was described by Bott (1955) as a subspecies of P. e m i n i ( Hilgendorf, 1892). Potamonautes semilunaris can nevertheless be easily distinguished from P. emini by the following characters: the postfrontal crest is distinct and complete in P. e m i n i but incomplete in P. semilunaris ; the terminal article of G1 is short and laterally directed with an upturned tip in P. emini but long, slim, and inwardly curved in P. s e m i - lunaris; the medial fold of the terminal article of G1 is higher than the lateral fold in P. e m i n i and the groove between the two is visible on the dorsal face, whereas the lateral and medial folds are low and even in P. semilunaris and the groove between them is not visible on the dorsal face; and by the uneven margins of the dorsal membrane of G1, which in P. e m i n i are narrower than the lateral margin and the proximal margin is U-shaped, whereas in P. semilunaris the medial and lateral margins are of equal width and the proximal margin is straight ( Reed and Cumberlidge 2006). In addition, P. semilunaris can be differentiated from P. gonocristatus and P. m i n o r by the mandibular palp, which lacks a small hard flap at the junction between the segments, and by the shape of the terminal article of G1, which is not widened in the middle in P. semilunaris but is widened in the middle in P. gonocristatus , P. m i n o r, and P. perparvus ( Table 1 ).

Figures

FIGURE 9. Potamonautes semilunaris. A, dorsal view; B, frontal view; C, sternal view. Adult male paratype (SMF 2429), CW 20.0 mm.

FIGURE 10. Potamonautes semilunaris. A, G 1, ventral view; B, G 1, dorsal view; C, G 2; D, detail of G 1, ventral view; E, detail of G 1, dorsal view. Adult male paratype (SMF 2429), length of G 1 terminal article measured along the mid-line of the dorsal face from tip to dorsal membrane = 0.9 mm.

FIGURE 11. Potamonautes semilunaris distribution. = type locality, = other localities. Scale bar = 63 km. Localities are shown for material examined in this study and in Bott (1955).