Potamonautes infravallatus ( Hilgendorf, 1898 )

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

3. Potamonautes infravallatus ( Hilgendorf, 1898) (Figs. 23–30, 149–150, 175, plate III)

Telphusa infravallata Hilgendorf, 1898: 12–13 , fig 2, 2a.

Potamon (Potamonautes) infravallata — Rathbun, 1905: 174.

Potamon (Potamonautes) usambarae Rathbun, 1933: 257 , pl. 6; Chace, 1942: 189, fig. 2.

Potamon infravallatus — Chace, 1942: 213.

Potamonautes (Rotundopotamonautes) infravallatus — Bott, 1955: 293–294, pl. XXV, fig. 2a–d, fig. 57.

Type material examined: TANZANIA: Telphusa infravallata: Usambara Mountains, Buloa , adult male type (cw 23.4, cl 15.4, ch 7.4, fw 6.5 mm) ( ZMB 11378); Potamon (Pot­

amonautes) usambarae : male subadult cotype (cw 22.4, cl 16.8, ch 6.8, fw 6.0 mm); female subadult cotype (cw 12.2, cl 9.5, ch 4.9, fw 3.6 mm), East Usambara Mountains, Amani, xii.1926 (A. Loveridge) ( MCZ 7680).

Additional material examined: TANZANIA: East Usambara Mountains , Amani, female (damaged), male (damaged), 8.xii.1926 (A. Loveridge) ( USNM 64108 ) ; Amani , East Usambara mountains, 2 males (cws 17.1, 18.2 mm), 1.i.1964 (J. N. Raybould) ( NMU TRW1964.03 b) ; East Usambara Mountains , Amani, 3 males (cw 19.8 to cw 22 mm), adult female (cw 24.1 mm), 2 subadult females (cws 19.8, 21.4 mm), v.1966 (J. N. Raybould) ( NMU TRW1966.12 a) ; West Usambara Mountains , Milinga River , Tewe near Mlalo, adult female (cw 22.8 mm), 18.ii.1967 (J. N. Raybould) ( NMU TRW1967.11 ) ; East Usambara Mountains , Amani, 3 juvenile males (cw 10.9 to cw 12.1 mm), 3 juveniles (cw 9.8 to cw 12.2 mm), 3 juvenile females (cw 12.8 to cw 14.2 mm), 6 males (cw 15 to cw 18.4 mm), 3 subadult females (cw 16.9 to cw 17.3 mm), 2 adult females (cw 17.8 to cw 18.4 mm), subadult female (damaged), ( NMU TRW1970.06 ) ; 4 subadult females (cw 15.9 to cw 18.2 mm), 7 males (cw 14.7 to cw 18.6 mm), 9.iii.1972 ( NMU 09.03.1972) ; West Usambara Mountains , 3 km north of Mazumbai, 1 specimen, 13.ii.1975, (Dunbar) ( NMU TRW1975.01 ) .

Diagnosis. Postfrontal crest distinct, granulated, complete; exorbital tooth small, low; epibranchial tooth small, granular, anterolateral margin immediately behind epibranchial tooth lined by granules; ischium of third maxilliped with deep vertical sulcus; thoracic sternal sulcus s3/s4 deep at sides, shallow across middle; sternite s4 with raised rounded marginal ridges at points where chelipeds articulate; dactylus of major cheliped of adult males slender; first carpal tooth on carpus of cheliped sharp spine; second carpal tooth sub­equal spine, followed by one or two small teeth; ventral margins of merus of pereiopod 1 both lined by large granules; distal meral tooth large, pointed; terminal article of gonopod 1 short, stout, tapering cone, in line with longitudinal axis of gonopod; terminal article of gonopod 1 covered entirely by fields of short spines or stiff bristles; lateral, medial folds both low, of equal size; dorsal membrane not visible.

Size. Small, with an adult size range beginning at cw 23 mm.

Type locality. Telphusa infravallata: Buloa, Usambara Mountains , Tanzania ; P. usambarae: Amani, Usambara Mountains , Tanzania.

Distribution. East and West Usambara Mountains, Tanzania.

Remarks. Identification of P. infravallatus was based on examination of the adult male type of Telphusa infravallata Hilgendorf, 1898 (cw 23.4, cl 15.4, ch 7.4, fw 6.5 mm) (ZMB 11378). Bott (1955) synonymized P. infravallatus with Potamon (Potamonautes) usambarae Rathbun, 1933 , and this is accepted here following comparison of P. infravallatus to the male cotype of P. (P.) usambarae from the Usambara Mountains (cw 22.8 mm) (MCZ 7680).

Natural history and conservation status. The conservation status of P. infravallatus 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 (despite the material presented here), based on indirect measures such a relatively poor representation in museum collections and increasing habitat disturbance associated with growing human populations in the region.