Potamonautes pilosu

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

8. Potamonautes pilosu s ( Hilgendorf, 1898) (Figs. 72–81, 159–160, 180, plate VIII)

Thelphusa pilosa Hilgendorf, 1898: 17–18 .

Potamon pilosum — de Man, 1898: 437.

Potamon (Geothelphusa) pilosus — Rathbun, 1905: 210.

Potamon pilosus — Chace, 1942: 219.

Potamonautes (Platypotamonautes) pilosu s— Bott, 1955: 237–238 (part only, not Figs. 16, 68, Pl. V, 1a–d).

Type material examined: TANZANIA: Telphusa pilosa subadult male lectotype (cw 22.8, cl 15.7, ch 7.9, fw 5.8 mm), rain forest near Marangu (= Maranga), 3°17'S, 37°31'E, Morogoro District, at the base of Mount Kilimanjaro ( ZMB 11387) .

Additional material examined: TANZANIA: Kilimanjaro, Marangu, Monju River , 2,730 m asl, rocky river in forest, male (cw 26.2 mm) 2.iii.1975 (J. Grunewald) ( NMU 1975.09 ) . KENYA: Namanga Hill , river campsite, 1,768 m asl, 2°31’S, 36°47’E, adult male (cw 38.5 mm) 23.iii.1986 ( NNM) ; Namanga Hill , river campsite, 1,768 m asl, 2°31’S, 36°47’E, female subadult (cw 36.7 mm) 23.iii.1986 ( NNM) ; Namanga Hill , river campsite, 1,768 m asl, 2°31’S, 36°47’E, female subadult (cw 32.8 mm) 23.iii.1986 ( NNM) ; Kibwesi ( NNM) ; Kilimanjaro area near Taveta, junction of Mue & Mwenda Rivers, 6–7 m wide, many large boulders, stones in between, embedded in silty sand, occasional stony­gravelly riffles, in a deeply shaded gully in forest, adult male (cw 30.2 mm) from unshaded pool, 5 juveniles from riffles (cw 7.1 to cw 12.9 mm) 3.iii.1962 ( NMU TRW­EA62.66) .

Diagnosis. Postfrontal crest incomplete, not completely crossing carapace, distinct gap between raised epigastric crests; ends of crest raised where it meets anterolateral margins; exorbital tooth low, epibranchial tooth absent; anterolateral margin behind epibranchial tooth granulated, fading posteriorally; all three regions of carapace sidewalls smooth; sternal sulcus s3/s4 incomplete consisting of short deep sections at sides, but sulcus absent in middle; lateral margins of s4 not thickened or raised; episternal sulci s4/e4, s5/e5, s6/e6, s7/e7 all faint, incomplete; ischium of third maxilliped with deep vertical sulcus; lower margin of propodus of major cheliped of adult males elongated, longer than carapace width; first carpal tooth of P1 large, pointed, second carpal tooth short, pointed, followed by 2 small granules; merus of cheliped elongated, dactylus highly arched, enclosing oval interspace; terminal article of gonopod 1 curving outward at 45° angle to longitudinal axis of gonopod; proximally, terminal article broad lateral fold higher than medial fold, distally article narrow, tip curving upward; distal margin of subterminal segment distinctly widened on medial side (forming rounded shoulder) narrow on lateral side; dorsal membrane very broad on lateral side where membrane clearly separates terminal article from subterminal segment; dorsal membrane narrow on medial side where these two structures meet.

Size. A medium sized species with a pubertal molt occurring around cw 37 mm.

Type locality. Rain forest near Marangu (= Maranga), Morogoro District , at the base of Mount Kilimanjaro, Tanzania .

Distribution. Along the border between Kenya and Tanzania.

Remarks. The lectotype of Telphusa pilosa is a subadult male (cw 22.8, cl 15.7, ch 7.9, fw 5.8 mm) (ZMB 11387) that was figured by Bott (1955) and examined in the present study. Bott (1955) synonymized P. pilosus with Potamon (Potamonautes) odhneri Colosi, 1924 . Our opinion is based on our examination of a series of specimens from two localities in Kenya and a topotypal specimen from Tanzania. Comparison of a female syntype of Potamon (Potamonautes) odhneri from near Meru, Kenya (SMNH 11852) with the type of P. pilosus raises doubts about the validity of Bott’s (1955) synonymy which is not accepted here. It should be noted that Bott’s (1955) photographs of P. pilosus (Pl. V, 1a–d) show the female paratype of P. (P.) odhneri Colosi, 1924 (SMNH 6430, cw 23, cl 17, ch 10, fw 7.5 mm) from Limuru, near Mount Kenya, Kenya, and not the lectotype of T. pilosus . Potamonautes pilosus is similar to P. neumanni from southern Kenya, but the two taxa can be distinguished by the following characters: in P. neumanni the sternal sulcus s3/s4 is complete and crosses the sternum, and the lateral margins of sternite s4 are raised, thickened, and rounded at the points where the chelipeds articulate.

Natural history and conservation status. The conservation status of P.pilosus is categorized as vulnerable (VU) ( Table 4) because it has a narrow range of occurrence and a restricted area of occupancy that are both below the thresholds for vulnerable (VU) ( IUCN 2004). It is difficult to estimate the population status and trends of this species, but its population is estimated to be declining based on indirect measures such as lack of recent collections of specimens, a relatively poor representation in museum collections and increasing habitat disturbance associated with growing human populations in the region.