Potamonautes lirrangensis ( Rathbun, 1904 )

Cumberlidge, Neil, Johnson, Emily, Clark, Paul F. & Genner, Martin J., 2021, Unravelling the Potamonautes lirrangensis (Rathbun, 1904) species complex (Potamoidea: Potamonautidae), with the description of two new species, European Journal of Taxonomy 744 (1), pp. 145-178 : 153-156

Potamonautes lirrangensis ( Rathbun, 1904) sensu stricto Figs 1 , 4A , 7A , Table 1

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

Potamon (Potamonautes) lirrangensis – Rathbun 1905: 169; 1921: 413–415, pls 25, 26 figs 3, 8. — Balss 1914: 404; 1929: 347–348 (partim, nec D.R. Congo: Kituri upper Lualaba, Katanga Province, Russisi River, Lake Kivu); 1936: 188–189 (partim, nec D.R. Congo: Banana, Lakes Kivu, Mweru).

Potamon lirrangensis – Chace 1942: 188–189. — Capart 1954: 836, fig. 28.

Potamonautes (Lirrangopotamonautes) lirrangensis – Bott 1955: 268–269 (partim, nec Lake Kivu, Kindu, Lokandu, Kinshasa, Buta, Lubo, Lulua, Luzizi, Ruzizi Rivers, Luvungu, Lake Tanganyika (Mpala, Uvira), Lake Malawi).

Potamonautes lirrangensis – Cumberlidge 1998: 201 (partim, nec Tanzania: Tukuyu formerly Neu- Langenburg). — Reed & Cumberlidge 2006: 23 (partim, nec figs 41–51, 153–154, 177 pl. V, Malawi: Lake Malawi, nec Tanzania: Kigoma District, rivers draining into Lake Tanganyika, Taveta, Mungonya River, Uvinza, Malagarasi River). — Ng et al. 2008: 171 (partim).

Diagnosis

Based on female type from Liranga. Exorbital tooth large, spine-like; lateral margin of exorbital tooth lined by small teeth, angled outward at 45 ° to midline of carapace, straight, neither bulging outward (convex) nor curving inward (concave); epibranchial tooth small, pointed, as large as other denticles lining anterolateral margin ( Fig. 4A ). Anterolateral margin posterior to epibranchial tooth curving strongly outward ( Fig. 4A ); postfrontal crest distinct, completely traversing carapace between epibranchial teeth; posterior surface of carapace with deep urogastric grooves; cheliped carpus inner margin with two large, subequal, forwardpointing spines ( Fig. 7A ); cheliped merus inner lower margin with spine-like tooth distally.

Material examined

Holotype (by original designation)

REPUBLIC OF THE CONGO • 1 ♀ adult (dried, CW 43.7, CL 38, FW 14.5 mm); Liranga , Middle Congo River , at the confluence of the Congo and Oubangi Rivers; 5 Sep. 1891; J. Dybowski leg.; MNHN B-3826 .

Description

See Diagnosis.

Size

Medium-sized species, adult at CW 43 mm.

Colour

The preserved specimen from Liranga is uniformly light brown.

Distribution

The revised distributional range of P. lirrangensis s. str. ( Fig. 1 ) now comprises just the Middle Congo River: Liranga (not ‘Lirranga’ as implied from the specific epithet) in the République du Congo. This species now excludes specimens formerly identified as P. lirrangensis s. lat. from Kisangani in the D.R. Congo ( Fig. 1 ), rivers near Kigoma draining into Lake Tanganyika, in Tanzania, Lake Tanganyika in Zambia ( Fig. 3 ), and Lake Malawi in Malawi ( Fig. 2 ).

Ecology

The type locality of P. lirrangensis s. str. in the Middle Congo River (Liranga) lies in the Sudanic Congo-Oubangi Ecoregion (Freshwater Ecoregions Of the World (FEOW #535) ( Thieme et al. 2005; Abell et al. 2008). This is more than 1000 km from Kisangani where Potamonautes kisangani sp. nov. is found in the Upper Congo Rapids Ecoregion (FEOW # 539), which indicates that the habitats of these 2 taxa are different, despite both being located in the Middle Congo River. Interestingly, these 2 taxa are separated by a third ecoregion, the Cuvette Centrale (FEOW #537).

Comparisons

Taxonomically important characters of the male cheliped, thoracic sternum, and gonopods, and the colour when alive, together with DNA data for P. lirrangensis s. str. will not be available until topotypal material is collected that includes an adult male. The carapace of the female type specimen from Liranga was illustrated by Capart (1954: fig. 28) and photographed by Rathbun (1904: pl. 14 fig. 8) and (together with the cheliped carpus) have been included in the present study ( Figs 4A , 7A ).

The lateral margin of the exorbital tooth of P. lirrangensis s. str. from Liranga ( Fig. 4A ) is similar to that of P. kisangani sp. nov. from Kisangani ( Fig. 4B ; Rathbun 1904: fig. 8a) and is angled outward at 45° to the midline of the carapace and is straight and neither bulges outward (convex) nor curves inward (concave). This contrasts with that of P. amosae sp. nov. from Lake Kivu ( Fig. 4C ) and the Malagarasi River ( Reed & Cumberlidge 2006: pl. 5a), where the lateral margin of the exorbital tooth is not straight and bulges distinctly outward (convex) before meeting the postfrontal crest. This also contrasts with P. orbitospinus from Lake Malawi ( Fig. 4E ) where the lateral margin of the exorbital tooth curves inward (concave) and is neither straight nor convex.

The identifications of specimens as P. lirrangensis s. lat. by a number of authors ( Rathbun 1921; Chace 1942; Bott, 1955; Reed & Cumberlidge 2006; Cumberlidge & Meyer 2011) are all now considered unreliable because they conflate characters from the 4 taxa that comprise the species complex under study here. Specifically, the descriptions of the male characters of P. lirrangensis s. lat. by the above authors combined characters from specimens from Kisangani, Lake Kivu, Tanzania, and Lake Malawi ( Table 1 ).

Three taxonomic consequences of the treatment of P. lirrangensis s. lat. by Bott (1955) are addressed here. For example, that Bott (1) established the subgenus Potamonautes (Lirrangopotamonautes) Bott, 1955 with Potamon (Potamonautes) lirrangensis from Liranga, Middle Congo River as the type species; (2) included 3 taxa in this subgenus: Potamonautes (Lirrangopotamonautes) lirrangensis , P. (L.) j. johnstoni (Miers, 1885) and P. (L.) johnstoni platycentron Hilgendorf, 1897 ; and (3) treated Potamon (Potamonautes) orbitospinus as a junior synonym of P. (L.) lirrangensis . The subgenus Potamonautes (Lirrangopotamonautes) Bott, 1955 , however, has not been recognized by subsequent authors due to doubts about the monophyly of a group comprising these 3 taxa ( Reed & Cumberlidge 2006; Ng et al. 2008). Currently, P. johnstoni ( Reed & Cumberlidge 2006: 21–23, figs 31–40, 151–152, 176 pl. IV) and P. platycentron ( Reed & Cumberlidge 2006: 30–31, figs 82–92, 161–162, 181 pl. IX) are each recognized as valid species, while the taxonomic status of P. orbitospinus is addressed in the present study.

Conservation status

The current IUCN extinction risk assessment of LC for P. lirrangensis s. lat. was based on the extremely wide range of that taxon ( Cumberlidge 2018). The present work reduces the range of P. lirrangensis s. str. significantly ( Fig. 1 ), from an estimated extent of occurrence (EOO) of almost 1.5 million km 2 based on 58 localities, to a single locality that precludes the calculation of the EOO. This change will no doubt impact the conservation assessment of this species when it is revised.

Figures

Fig. 1. Map showing the updated geographic distribution of Potamonautes lirrangensis (Rathbun, 1904) s. str. The black star on the left is Liranga, République du Congo (MNHN B-3826), the type locality. The black circles show the distribution of Potamonautes kisangani sp. nov. in the vicinity of Kisangani, D.R. Congo. See text for exact localities.

Fig. 4. Dorsal view of the right side of the carapace. A. Potamonautes lirrangensis s. str., holotype, adult, ♀, CW 53.6 mm, from Liranga, République du Congo (MNHN B-3826) (Capart 1954: fig. 28). B. P. kisangani sp. nov., holotype, adult, ♂, CW 60.5 mm, from Kisangani, Democratic Republic of the Congo (USNM 98944). C. P. amosae sp. nov., holotype, adult, ♂, CW 46.5 mm, from Lake Kivu, D.R. Congo (NHMUK 2018.306). D. P. amosae sp. nov., adult, ♂, CW 39.5 mm, from Kigoma District near Lake Tanganyika, Tanzania (NMU TRW 1971.05). E. P. orbitospinus (Cunnington, 1907), lectotype, adult, ♂, CW 56.9 mm, from Nkhata Bay, Lake Malawi, Malawi (NHMUK 1908.1.31.27). Scale bar: A = 8.7 mm; B = 7.9 mm; C = 6.8 mm; D = 5.7 mm; E = 7.9 mm. Photograph E by Phillip Crabb, NHMUK.

Fig. 7. Dorsal view of right cheliped carpus. A. Potamonautes lirrangensis s. str., holotype, adult, ♀, CW 53.6 mm, from Liranga, République du Congo (MNHN B-3826) (Rathbun, 1904: pl. 14, fig. 8). B. P. kisangani sp. nov., holotype, adult, ♂, CW 60.5 mm, from Kisangani, Democratic Republic of the Congo (USNM 98944). C. P. amosae sp. nov., holotype, adult, ♂, CW 46.5 mm, from Lake Kivu, D.R. Congo (NHMUK 2018.306). D. P. orbitospinus (Cunnington, 1907), lectotype, adult, ♂, CW 56.9 mm, from Nkhata Bay, Lake Malawi, Malawi (NHMUK 1908.1.31.27). Scale bar: A = 5.7 mm; B = 4.8 mm; C = 3.6 mm; D = 4.9 mm. Photograph D by Phillip Crabb, NHMUK.

Fig. 3. Map showing the updated geographic distribution of Potamonautes amosae sp. nov. The black star shows the type locality. See text for exact localities.

Fig. 2. Map showing the updated geographic distribution of Potamonautes orbitospinus (Cunnington, 1907). The black star shows the type locality. See text and Table 2 for exact localities.