Potamonautes emini ( Hilgendorf, 1892 )

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

1. Potamonautes emini ( Hilgendorf, 1892) (Figs. 1–11, 145–146, 173, plate I)

Thelphusa emini Hilgendorf, 1892: 11 ; 1898: 17–18.

Potamon Emini — de Man, 1898: 436; Capart, 1954: 832, figs. 19, 32.

Potamon (Geothelphusa) Emini — Rathbun, 1904: pl. 18, fig. 9; 1905: 209; 1909: 102; 1922: 35; Lenz, 1910: 5; Bouvier, 1921: 50, fig. 4.

Potamon (Potamonautes) emini — Balss, 1929: 345.

Geothelphusa emini — Balss, 1936: 193, fig. 28.

Potamon emini — Chace, 1942: 193.

Potamonautes (Rotundopotamonautes) emini emini — Bott, 1955: 280–291, pl. 24, fig. 1a–d, fig. 54.

Potamonautes emini — Cumberlidge, 1997: 581; 1998: 199.

Type material: TANZANIA: Telphusa emini Hilgendorf, 1898 , male lectotype (cw 15.4, cl 10.4, ch 5.1, fw 5.1 mm) ( ZMB 8406 ), preserved dry, Bukoba .

Additional material examined: TANZANIA: Bukoba District , on Bukoba­Biharamulo road, 8 km from Bukoba , Wazi River , Bungonzi stream (small), Ndolage, 1,417 m, 4 adult females (cw 27.2 to cw 36.5 mm; 2 damaged), 12 males (cw 22.1 to cw 33.2 mm), 1967 (A. W. R. McCrae) ( NMU TRW1967.01 ) ; Bukoba District , Kyarubamba River near Pantelukis, 3 adult females (cw 25 to cw 27.7 mm), adult male (cw 29.7 mm), 2 subadult males (cw 22.9, cw 23.9mm), subadult female (cw 22.6 mm), juvenile female (cw 18.3 mm), 10.xii.1966 (A. W. R. McCrae) ( NMU TRW1967.02 ) ; Bukoba District , on Bukoba­ Biharamulo road, 8 km from Bukoba, Wazi River, adult female (cw 32.4 mm), 2 adult males (cw 28.2, cw 31.5 mm), 5.xii.1966 (A. W. R. McCrae) ( NMU TRW1967.03 a) ; Bukoba District , on Bukoba­Biharamulo road, 8 km from Bukoba, Wazi River, 10 adult females (cw 27 to cw 32 mm), 6 subadult females (cw 24.2 to cw 26.8 mm), 8 juvenile females (cw 21 to cw 23 mm), 5.xii.1966 (A. W. R. McCrae) ( NMU TRW1967.03 b) ; Bukoba District , Kanyamugua River, 5 adult females (cw 26 to cw 30.6 mm), 2 subadult females (cw 25.7, 27.1 mm), 6 males (cw 24.4 to cw 30.1 mm), 2 juvenile males (cw 20.5, 21.4 mm), 2 juvenile females (cw 23.1, 23.6 mm), 7.xii.1966 (A. W. R. McCrae) ( NMU TRW1967.04 a) ; Bukoba District , Kanyamugua River, adult female (cw 30.3 mm), 4 adult males (cw 25.8 to cw 29.4 mm), 3 juvenile males (cw 21.8 to cw 22.8 mm), 3 subadult females (cw 24.4 to cw 25.9 mm), juvenile female (cw 21.4 mm), 7.xii.1966 (A. W. R. McCrae) ( NMU TRW1967.04 b) ; Bunyaro District , Upper Waki River, Nyantonzi area, adult female (cw 27.1 mm), 2 males (cw 24.7, 25.9 mm), 18.viii.1965 (A.W. R McCrae) ( NMU TRW1966.16 ) ; Bukoba District , Kanyamugua River at foot of plateau, 2 adult females (cw 31.5, 34.3 mm), male (cw 25.4 mm), juvenile female (cw 20 mm), 7.xii.1966 (A. W. R. McCrae) ( NMU TRW1967.00) ; UGANDA: Ugungwe Mountains , Kigoya, ovigerous female (cw 17.6 mm), i.1930 (A. Loveridge) ( USNM 64109 ) . DEMOCRATIC REPUBLIC OF THE CONGO: Kisangani , male (cw 18.5 mm) ( USNM 102264 ) .

Diagnosis. Postfrontal crest distinct; epibranchial tooth absent; exorbital tooth low; grooves on posterior carapace faint; anterolateral margin continuous with posterolateral margin; all 3 regions of carapace sidewalls smooth; s3/s4 incomplete, deep at sides, faint across middle; margins of s4 raised, rounded where chelipeds insert; episternal sulcus s4/ e4 absent, s5/e5, s6/e6, s7/e7 complete; ischium of third maxilliped with vertical sulcus; dactylus of adult male major cheliped slender, arched, enclosing oval interspace; first carpal tooth of cheliped large spine, second carpal tooth small, with another small tooth behind it; medial inferior margin granulated with large rounded distal meral tooth surrounded with granules, lateral inferior margin granulated; first half of terminal article of gonopod 1 straight with parallel sides, angled slightly outward, second half curving sharply outward, tapering gently to broad tip; terminal article of gonopod 1 not significantly widened in middle, lateral, medial folds low, evenly sized; base of terminal article concave at dorsal membrane; distal margin of subterminal segment concave at dorsal membrane; the dorsal membrane broad at lateral margin, tapering to point at medial margin.

Size. Small, with an adult size range from cw 17.6 to cw 36.5 mm.

Variation. The chelipeds of P. emini undergo allometric growth in males, whereby the dactylus of the major cheliped is straight in young crabs, becoming arched in adults, where the entire major cheliped is much longer and higher than the minor cheliped. Heterochely is also seen in female crabs but the dramatic arching of the dactylus is absent.

Type locality. Bukoba Bay , Tanzania .

Distribution. Tanzania, Democratic Republic of Congo, Uganda, Rwanda.

Remarks. The male lectotype of Telphusa emini Hilgendorf, 1898 (cw 15.4, cl 10.4, ch 5.1, fw 5.1 mm) (ZMB 8406) is preserved dry and was photographed by Bott (1955: fig. Pl. XXIV, fig. 1a–d). Identification of specimens in the present work was based on comparisons with a subadult male paratype (cw 14.2, cl 9.8, ch 4.8, fw 4.12 mm) (ZMB 11384) from Bukoba, Tanzania. Bott (1955) synonymized P. (G.) mutandensi s Chace, 1942 from Lake Mutanda in Uganda and from Lake Kivu in Rwanda with P. emini , but this opinion is not supported here because of distinct differences in characters of the first gonopod of the types of these two taxa examined here.

Natural history and conservation status. Potamonautes emini is a widespread and abundant species that has been collected recently. A. W. R. McCrae’s field notes record P. emini from streams where the water flow was slow, almost stagnant, with iron oxide flocculates on the streambed. This species was also collected from underneath rocks and cobbles in fast flowing streams near Lake Tanganyika (S. Marijnissen, pers. comm). The conservation status of P. emini is categorized as least concern (LC) ( Table 4) because both the range of occurrence and the area of occupancy are in excess of the thresholds for vul­ nerable (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 relatively recently from more than one locality (present study, S. Marijnissen, pers. comm.) and that this species is well represented in museum collections