Diyutamon n. gen.

(Figs. 1 A, 2–7)

Diagnosis. Carapace subtrapezoidal, dorsal surface gently convex, appearing almost flat in frontal view, smooth, regions barely indicated (Figs. 2 A, B, 3A, 7A); frontal margin not prominently protruding anteriorly; postorbital, epigastric cristae not distinct (Figs. 2 A, 3A, 7A); external orbital angle broadly triangular, almost confluent with anterolateral margin (Figs. 2 A, B, 3A–D, 7A); median lobe of posterior margin of epistome broadly triangular (Figs. 2 B, 3B, D); third maxilliped with relatively broad ischium, exopod reaches beyond anterior edge of ischium, with long flagellum (Fig. 5 D); pollex of male, female major chela with basal molariform tooth on cutting edge (Figs. 4 C, 7C); male thoracic sternite 8 exposed when abdomen closed (Figs. 2 C, 3E, F); male abdomen triangular, telson with almost straight lateral margins, rounded tip (Figs. 2 C, 3E); G1 generally slender, terminal segment slightly curved upwards, tapered (Figs. 5 A, C, 6A, B); basal segment of G2 subrectangular (Fig. 5 B).

Etymology. The genus name is derived from the Chinese word Diyu, for hell, which alludes to the subterranean habitat of the type species. The suffix is derived from “ Potamon ”, the type genus of the family. Gender of genus neuter.

Remarks. Although Diyutamon n. gen., is superficially similar to Chinapotamon and Tiwaripotamon, it can easily be distinguished in possessing almost undiscernible postorbital cristae, the external orbital angle is confluent with the anterolateral margin which is lined with small spines and sharp granules, the ambulatory legs are conspicuously long and slender, and most significantly, the edge of thoracic sternite 8 remains visible even when the abdomen is closed (Table 1). While the strongly reduced eyes, with short peduncles, and small corneas without pigmentation (Figs. 2 B, 3B, D), are very diagnostic features of the type species (not known for any species of Chinapotamon or Tiwaripotamon), these are probably highly derived characters associated with its stygobitic habits. As such, they are probably not phylogenetically significant (see Ng & Sket 1996; Klaus et al. 2013).