Deckeniidae Ortmann 1897

FAMILY DECKENIIDAE ORTMANN, 1897

(FIGS 1, 11A–C; TABLES 1–3)

Diagnosis: Deckeniidae taxa are recognized by characters of the second gonopod (G2). When the G2 is viewed in cross section the dorsal side of the SA-TA junction has a setose spoon-like structure. When the G2 TA is viewed in cross section the dorsal margin is either lacking or it is extremely reduced. The G2 TA is long and flagellum-like, with a ventral margin that is folded to create a tube, but the degree of folding varies from completely open (Afrithelphusa), to partly closed (Seychellum), to almost closed (Hydrothelphusa, Malagasya and Madagapotamon). For Deckeniiidae taxa the G2 TA flagellum is never a completely closed tube as in Potamon (Klaus et al., 2006).

Type genus: Deckenia Hilgendorf, 1869, by original designation.

Genera included: Afrithelphusa Bott, 1969, Agora Cumberlidge, Soma, Leever & Daniels, 2020, Boreathelphusa (Cumberlidge & von Sternberg, 2002), Deckenia Hilgendorf, 1869, Foza Reed & Cumberlidge, 2006b, Glabrithelphusa Meyer et al., 2014, Globonautes Bott, 1959, Hydrothelphusa A. Milne-Edwards, 1872, Madagapotamon Bott, 1965, Malagasya Cumberlidge & von Sternberg, 2002, Marojejy Cumberlidge, Boyko & Harvey, 2002, Seychellum Ng et al., 1995 and Skelosophusa Ng & Takeda, 1994.

Distribution: Deckeniidae taxa are found in West Africa (Liberia, Guinea, Sierra Leone), East Africa (Tanzania, Kenya, Somalia), the granitic Seychelles and Madagascar (Cumberlidge, 1999; Cumberlidge et al., 2004; Reed & Cumberlidge, 2006a, b; Fig. 11A–C).

Remarks: The Afrotropical freshwater crabs form a well-supported monophyletic group with two distinct lineages (Daniels et al., 2006, 2015) that are here recognized as two families, namely Potamonautidae and Deckeniidae (Tables 1–3), rather than two subfamilies (Cumberlidge et al., 2008). The revised Potamonautidae has two phylogenetic divisions (subfamilies): Potamonautinae (Tables 2, 3) from sub- Saharan Africa, except West Africa (Fig. 8A) and the new subfamily Liberonautinae (Fig. 7B) from West and Central Africa. The revised Deckeniidae has two lineages (subfamilies): Deckeniinae (type genus: Deckenia) (Tables 2, 3) from West Africa, East Africa and the Seychelles, formerly Deckeniini (Cumberlidge et al., 2008; Fig. 11B), and Hydrothelphusinae (type genus: Hydrothelphusa A. Milne-Edwards, 1872) from Madagascar, formerly Hydrothelphusini (Cumberlidge & von Sternberg, 2002; Cumberlidge et al., 2008; Cumberlidge, 2021; Fig. 11C).

Earlier authors (Bott, 1955; Martin & Davis, 2001) recognized the family Deckeniidae for one genus (Deckenia) with two species (Deckenia imitatrix and Deckenia mitis), which was included in the African Potamonautidae. Later, Klaus et al. (2006) expanded Deckeniidae to include six genera assigned to three subfamilies: Deckeniinae (Deckenia, Seychellum), Globonautinae (Afrithelphusa, Globonautes) and Hydrothelphusinae (Hydrothephus, Madagapotamon), which they assigned to the Asian superfamily Gecarcinucoidea.