Platythelphusa, A. Milne-Edwards, 1887

Cumberlidge, Neil & Daniels, Savel R., 2022, A new multilocus phylogeny reveals overlooked diversity in African freshwater crabs (Brachyura: Potamoidea): a major revision with new higher taxa and genera, Zoological Journal of the Linnean Society 194 (4), pp. 1268-1311 : 1295-1296

GENUS PLATYTHELPHUSA A. MILNE- EDWARDS, 1887

( FIGS 1B 3 [3], 5J–L, 10C; TABLES 1–3 )

Platythelphusa A. Milne-Edwards, 1887: 146 ; Hilgendorf, 1898: 21; Moore, 1903: 286; Rathbun, 1905: 268; Cunnington, 1907: 266–268; 1920: 557; Alcock, 1910: 253–261; Colosi, 1920: 9–10; Balss, 1936: 196; Chace, 1942: 224; Cumberlidge, 1999: 16, 17, 25, 36, 37, 42, 45, 66–69, 74, 76–79, 100–113, 116, 317; 2008: 72, 77, tab. 1; 2011: 79, 82–83, tabs 6.1, 6.3; Cumberlidge et al., 1999: 1491–1493; Marijnissen et al., 2004: 515; Ng et al., 2008: 171.

Limnothelphusa Cunnington, 1899: 698 ; Moore, 1903: 280; Rathbun, 1905: 269.

Hydrothelphusa (Platythelphusa) Bouvier, 1917a: 615–621 ; 1917b: 657–659; 1921: 41.

Potamonautes (Platythelphusa) Bott, 1955: 226–229 ; Coulter, 1991: 253–257.

Potamonautes (Obesopotamonautes) Bott, 1955 : pl. XII: figs 1a–d, 17, 18, 79a, b (partim, for Potamon (Potamonautes) langi Rathbun, 1921 ; not Thelphusa obesa A. Milne-Edwards, 1868 (= Maritimonautes obesus ) or Potamon (Potamonautes) calcaratus Gordon, 1929 (= Maritimonautes calcaratus ).

Diagnosis: Third maxilliped ischium smooth, lacking vertical sulcus (or with faint vertical sulcus); thoracic sternal sulcus S3/4 deep, completely traversing sternum (or deep only at sides, faint in middle).

Distribution: Platythelphusa includes 11 species with a distribution centred on Lake Tanganyika and its drainage basin (in Malawi, Tanzania, D.R. Congo, Rwanda and Burundi), except for two species from the D.R. Congo: Platythelphusa langi from Tshopo Province and Platythelphusa idjwiensis from Lake Kivu in Nord-Kivu Province ( Cumberlidge et al., 1999; Marijnissen et al., 2004; Reed & Cumberlidge, 2006a; Cumberlidge, 2015; Fig. 10C ).

Type species: Platythelphusa armata A. Milne- Edwards, 1887, by monotypy.

Species included: Platythelphusa armata A. Milne- Edwards, 1887, Platythelphusa conculcata (Cunnington, 1907) , Platythelphusa denticulata Capart, 1952 , Platythelphusa echinata Capart, 1952 , Platythelphusa idjiwiensis ( Chace, 1942) comb. nov., Platythelphusa immaculata Marijnissen, Schram, Cumberlidge & Michel, 2004 , Platythelphusa langi ( Rathbun, 1921) comb. nov., Platythelphusa maculata (Cunnington, 1902) , Platythelphusa polita Capart, 1952 , Platythelphusa praelongata Marijnissen, Schram, Cumberlidge & Michel, 2004 , Platythelphusa tuberculata Capart, 1952 .

Remarks: The subgenus Potamonautes (Platythelphusa) Bott, 1955 is reestablished, revised and given genus status here to accommodate 11 species: all nine Platythelphusa species from Lake Tanganyika, plus Pl. langi (now Platythelphusa ) from the Upper Congo Basin in the D.R. Congo and Pl. idjwiensis (now Platythelphusa ) from Lake Kivu. Daniels et al. (2015: fig. 1), Daniels & Klaus (2018: fig. 1) and Wood et al. (2019: fig. 1) and the present study ( Fig. 1B 3 ) all group these species together in a well-supported clade within the Potamonautini . Platythelphusa has two clear lineages within it, with one branch for the nine species endemic to Lake Tanganyika, and the other branch for species from the Upper Congo Basin in the D.R. Congo (including Lake Kivu).

Bott (1955) established the subgenus Po. ( Platythelphusa ) for Po. (Pl.) armata armata and Po. (Pl.) a. conculcata . The genus as revised here retains the name Platythelphusa because it includes the type species Platythelphusa armata A. Milne-Edwards, 1887 . DNA data are available for ten of these species ( Daniels et al., 2015: fig. 1; Daniels & Klaus, 2018: fig. 1; Wood et al., 2019: fig. 1; Fig. 1B 3 ). The remaining species, Pl. denticulata , is included here based on shared morphological characters that conform to the generic diagnosis ( Cumberlidge et al., 1999). One of the species included here in Platythelphusa [ Potamon (Potamonautes) langi Rathbun, 1921 ] was assigned by Bott (1955) as the type species of the subgenus Potamonautes (Obesopotamonautes) Bott, 1955 . Despite this, the genus name for these species remains as Platythelphusa by priority because the type species of the latter genus ( Platythelphusa armata A. Milne-Edwards, 1887 ) was described before Potamon (Potamonautes) langi Rathbun, 1921 .

All but one species assigned to Platythelphusa share the following characters: a distinct postfrontal crest that completely traverses the carapace between the epibranchial teeth, a small exorbital tooth, an epibranchial tooth reduced to a small granule, one or more long, sharp teeth lining the anterolateral margin of carapace, and a cheliped carpus with two subequal long, sharp teeth. Pl. idjwiensis is included because of phylogenetic evidence that positions it in the same clade as the other congeners ( Fig. 1B 3 [3]) despite the fact that Pl. idjwiensis lacks a postfrontal crest, has a completely smooth anterolateral margin that lacks teeth, and has a small reduced proximal tooth on the cheliped carpus inner margin.

Figures

Figure 1. A, maximum clade credibility tree of the Afrotropical freshwater crab fauna based on four DNA loci with support values (posterior probabilities and bootstrap values of the ML analyses) with a geological timescale below the tree topology. Posterior probabilities> 0.95 pP (*above branch) and bootstrap values> 75% (* below branch) were regarded as statistically supported and are shown on the tree topology. Clade A, Liberonautinae, clade B, Potamonautinae, clade B1, Maritimonautini, clade B2, Erimetopini, clade B3, Potamonautini. B, detail of the maximum clade credibility tree of the Afrotropical freshwater crab fauna showing Clade B3 Potamonautini with the species included in the five genera within the tribe: Arcopotamonautes (B3[1]), Lirrangopotamonautes (B3[2]), Platythelphusa (B3[3]), Potamonautes s.s. (B3[4]) and Rotundopotamonautes (B3[5]).

Figure 3. Gonopods 1 and 2 of four genera in Liberonautinae. A–C, Buea asylos (Cumberlidge et al., 2019: fig. 7a, d; 8a); D–F, Potamonemus mambilorum (Cumberlidge et al., 2019: fig. 7b, e; 8b); G–I, Sudanonautes floweri; J–L, Louisea balssi (Mvogo Ndongo et al., 2018: fig. 5a–c, © Magnolia Press, reproduced with permission from the copyright holder). A, D, G, J, left G1 ventral view; B, E, H, K, left G1 dorsal view; C, F, I, L, left G2 ventral view. Scale bar: A, B, D, E, G, H, J, K = 2.0 mm, C, F, I, L = 1.8 mm.

Figure 10. Maps showing the distributional ranges of the five genera of Potamonautini. (A) Arcopotamonautes, (B) Lirrangopotamonautes, (C) Platythelphusa, (D) Potamonautes s.s. and (E) Rotundopotamonautes.