Potamonautes unisulcatus ( Rathbun, 1933 )

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

13. Potamonautes unisulcatus ( Rathbun, 1933) (Figs. 124–133, 169–170, 185, plate XIII)

Potamon (Potamonautes) johnstoni unisulcatus Rathbun, 1933: 255 , figs. 2–4, pl. 2.

Potamon unisulcatus — Chace, 1942: 223.

Potamonautes (Lirrangopotamonautes) johnstoni johnstoni — Bott, 1955: 265–267, pl. XV, fig. 2a– d, fig. 36a, b.

Type material examined: TANZANIA: Potamon (Potamonautes) unisulcatus Rathbun, 1933 : adult male type (cw 33, cl 21, ch 9, fw 10 mm) Bagilo , Uluguru Mountains ( MCZ 7678 a) .

Additional material examined: TANZANIA: Uluguru Mountains, Bunduki, Kitange­Tange River (tributary of Maeta River ), between small falls, 1933 m asl, 7 m wide, large boulders, gravel, stones and sand, 23.ii.1962 ( NMU TRW­EA62.45); Kitange­ Tange River , Bunduki , Uluguru Mountains , male (cw 30.1 mm), female (cw 27 mm), 3 juveniles (cw 15.9 to cw 17.1 mm), juvenile (damaged) ( NMU TRW­EA62.47); Uluguru Mountains , Bunduki , Kitange­Tange River (tributary of Maeta River ), female (cw 41.4 mm), male (31.7 mm), 3 juveniles (cw 15 to cw 18.3 mm), ( NMU TRW­EA62.50a); Songea District , Ruvuma region, Mkulusi near Kigonsera , male (cw 29.5 mm), female (cw 30 mm), juvenile male (cw 17 mm), 28.viii.1967 ( T. R. Williams ) ( NMU TRW1967.15 ) .

Diagnosis. Postfrontal crest sharp­edged, completely crossing carapace; posterolateral regions of carapace with carinae; exorbital tooth low but distinct, epibranchial tooth reduced to small granule; anterolateral margin behind epibranchial tooth heavily granulated; carapace sidewalls smooth, vertical (pleural) groove meeting anterolateral margin between exorbital, epibranchial teeth; ischium of third maxilliped lacking vertical sulcus; thoracic sternal sulcus s3/s4 faint at sides, missing in middle; episternal sulci s4/e4 missing, s5/e5, s6/e6, s7/e7 complete, but weak; dactylus of major cheliped of adult males broad, not arched; first carpal tooth on carpus of cheliped large sharp spine; second carpal tooth small spine, with no other teeth behind it; ventral margins of merus of pereiopod 1 both distinctly granulated; distal meral tooth small, pointed; terminal article of gonopod 1 curving outward, lateral fold highly curved in first third, medial fold low, distal part of gonopod 1 tapering to straight point; distal margin of subterminal segment u­shaped, highest at medial margin with small shoulder on medial side; dorsal membrane sub­oval, narrow at medial lateral margins.

Size. The adult size range is from cw 28.4 to cw 41.4 mm.

Type locality. Bagilo , Uluguru Mountains, Tanzania .

Distribution. Uluguru Mountains, Tanzania.

Remarks. Bott (1955) treated Potamon (Potamonautes) unisulcatus Rathbun, 1933 as a junior synonym of P. johnstoni ( Miers, 1885) . However, this view is not followed here following comparisons of the type specimen of P. (P.) unisulcatus , an adult male (cw 33, cl 21, ch 9, fw 10 mm) (MCZ 7678a) with the type of P. johnstoni ( Miers, 1885) . The first gonopod of P. (P.) unisulcatus (Figs. 169–170) is clearly very different from that of P. johnstoni (Figs. 151–152), so P. unisulcatus is removed from synonymy and recognized here as a valid species. The conservation status of P. unisulcatus 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 factors such as the lack of recent specimens, its poor representation in museum collections and increasing habitat disturbance from deforestation associated with growing human populations in the region.