Potamonautes lirrangensis ( Rathbun, 1904 )

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

5. Potamonautes lirrangensis ( Rathbun, 1904) (Figs. 41–51, 153–154, 177, plate V)

Potamon (Potamonautes) lirrangensis Rathbun, 1904 : pl. 14, fig. 8.

Potamon (Potamonautes) lirrangensis — Rathbun, 1905: 169; 1921: 413–415, pl. 25, 26, fig. 3, fig. 8.; Balss, 1914: 404; 1929: 374–348; Chace, 1942: 188–189, fig. 1.

Potamon (Potamonautes) orbitospinus Cunnington, 1907: 250–251 , pl. 16, fig. 1.

Potamonautes orbitospinus — Balss, 1929: 439, 1936: fig. 18.

Potamonautes lirrangensis — Balss 1936: 188–189, fig. 24

Potamon orbitospinus — Chace, 1942: 218.

Potamonautes (Lirranpotamonautes) lirrangensis — Bott, 1955: 268–270, pl. XVI, fig. 2a–d, fig. 38, 39, 83.

Type material examined: TANZANIA: Potamon (Potamonautes) lirrangensis Rathbun, 1904 : adult female type (cw 53.9, cl 37.8, fw 12 mm) from Lirranga, D. R. Congo, 5.ix.1891 (J. Dybowski) ( MNHN) .

Additional material Examined: TANZANIA: Kigoma area, Taveta, Mungonya River , male (cw 39.6 mm), juvenile female (cw 35.7 mm), 16.iv.1971 ( NMU TRW1971.05 ) ; Kigoma district, Uvinza, Malagarasi River , juvenile female (damaged), 20.iv.1971 ( NMU TRW1971.07 ) ; Kigoma district, Uvinza, Malagarasi River , adult female (cw 81 mm), 25.iv.1971 ( NMU TRW1971.15 ) . DEMOCRATIC REPUBLIC OF THE CONGO: Kisangani , 3 females (cw 45.1 to cw 59.8 mm), female ovigerous (cw 54.8 mm), iv.1915 (Herbert Lang) ( USNM 54306 ) ; Kisangani , 5 females (cw 36.8 to cw 51.9 mm), 2 males (cws 29.2, 60.2 mm), iv.1915 (Herbert Lang) ( USNM 54307 ) ; Lake Kivu at Kisenyi , in water at the shoreline, female (cw 26.9 mm), 12.v.1955 (Bredin Expedition­W. L. Schmitt) ( USNM 98937 ) ; male (cw 46.4 mm), (Bredin Expedition­W. L. Schmitt) ( USNM 98938 ) ; Kisangani, vicinity of Wagenia fishery, male (cw 59.1 mm), (Bredin Expedition­W. L. Schmitt) ( USNM 98939 ) ; Kisangani, rocky gorge of Tshope Falls , male (cw 40.4 mm), 2 females (cws 24.8, 40 mm), 19.iv.1955 (Bredin Expedition­W. L. Schmitt) ( USNM 98940 ) ; Kisangani, vicinity of Wagenia fishery, female (cw 53.6 mm), (Bredin Expedition­W. L. Schmitt) ( USNM 98941 ) ; Kisangani , 2 ovigerous females (cws 53.7, 56.5 mm), female (cw 62.6 mm), 20.iv.1955 (Bredin Expedition­W. L. Schmitt) ( USNM 98942 ) ; Kisangani , female with hatchlings (cw 60.1 mm), 20.iv.1955 (Bredin Expedition­W. L. Schmitt) ( USNM 98943 ) ; Kisangani, Wagenia fishery, 3 males (cw 39.4 to cw 60.9 mm), 10 females (cw 40.3 to cw 66.5 mm), 3 ovigerous females (cw 54.7 to cw 66.5 mm), 25.iv.1955 (Bredin Expedition, W. L. Schmitt) ( USNM 98944 ) . MALAWI: Lake Malawi, North of Monkey Bay under 91 m of water, female (damaged), 5.iv.1972 (D. H. Eades) ( NMU TRW1972.02 ) ; Lake Malawi, Monkey Bay , among rock in sand with little vegetation, male (cw 51.4 mm), 24.iii.1968 (D. H. Eades) ( NMU TRW1972.04 ) ; Lake Malawi, east and northeast of Monkey Bay, Lake Malawi , male (cw 46.5 mm), 23.v.1968 (D. H. Eades) ( NMU TRW1972.05 ) .

Diagnosis. Postfrontal crest distinct complete; grooves on posterior part of carapace deep; exorbital tooth large forward pointing spine, epibranchial tooth small spine; anterolateral margin behind epibranchial tooth curving strongly outward, then curving inward over posterolateral margin, lined by either large granules or small teeth; vertical sulcus on ischium of third maxilliped faint; thoracic sternal sulcus s3/s4 complete, deep at sides, shallow across middle; dactylus of major cheliped of adult male broad, curved; first carpal tooth on carpus of cheliped large sharp spine; second carpal tooth sharp spine smaller than first tooth; ventral margins of merus of pereiopod 1 both heavily granulated, distal meral tooth sharp spine; first half of terminal article of gonopod 1 straight with parallel sides angled slightly outward, second half bent sharply outward at 90° angle to longitudinal axis of gonopod tapering to broad upcurved tip; lateral side of terminal article of gonopod 1 significantly widened in middle by enlarged lateral fold; medial fold smaller lower in dorsal view; distal margin of subterminal segment at dorsal membrane deeply v­shaped; dorsal membrane broadest at medial margin, narrow at lateral margin.

Size. Large, with a pubertal molt starting around cw 52 mm (a series of six ovigerous females ranged from cw 53.7 to cw 81 mm).

Type locality. Lirranga , at the confluence of the Congo and the Oubangi Rivers, Democratic Republic of Congo.

Distribution. Upper reaches of the Congo River, Democratic Republic of Congo; Lake Kivu, Rwanda; Malagarasi River near Lake Tanganyika, Tanzania; Lake Malawi, Malawi.

Remarks. Our opinion is based on the direct examination of the adult female type of Potamon (Potamonautes) lirrangensis Rathbun, 1904 (cw 53.9, cl 37.8, fw 12 mm) from Lirranga, collected by J. Dybowski, 5.ix.1891, which was also illustrated by Capart (1954: fig. 28). Bott (1955) synonymized P. orbitospinosus Cunnington, 1907 from Lake Malawi with P. lirrangensis . Cunnington (1907) provided plates with the dorsal view of the entire animal and a series of frontal views of P. orbitospinosus . The characters described by Cunnington (1907) for P. orbitospinosus clearly correspond to those of P. lirrangensis , and this synonymy is accepted here.

Natural history and conservation status. The conservation status of P. lirrangensis is categorized as least concern (LC) ( Table 4) because it has a range of occurrence and area of occupancy that are both in excess of the thresholds for vulnerable (VU) ( IUCN 2004). Its population is estimated to be stable based on indirect measures such the fact that it has been collected recently from rocky areas in Lake Kivu and from small fast flowing rivers, as well as from large slow flowing rivers flowing into Lake Tanganyika (M. Mbalassa and S. Marijnissen, pers. comm). In addition, P. lirrangensis supports a local fishery in Lake Malawi, and this species is well represented in museum collections.