Genus Stephonyx Lowry & Stoddart, 1989

Euonyx . Stebbing, 1906: 19; Barnard, 1969: 342; Lincoln, 1979: 54. Stephonyx . Lowry & Stoddart, 1989: 521.

Type species. Euonyx biscayensis Chevreux, 1908

Diagnosis. Antenna 1: callynophore well developed in female and male. Mandible: incisors symmetrical, lacinia mobilis a well developed smooth or denticulate peg, accessory spine row with 5 or fewer small spines, molar setose with distal vestigial triturating surface. Maxilla 1: outer plate narrow, with 11 large, multicuspidate spine teeth which form a distal crown of 7 and a row of 4 extending down the medial face. Maxilla 2: inner plate shorter than outer. Maxilliped: outer plate large, subovate, simple apical setae and stout apical setae present, medial spines present, but extremely reduced in size. Gnathopod 1, chelate, coxa very reduced. Uropod 3: rami with plumose setae in female and male (modified after Lowry & Stoddart, 1989).

Species composition. contains 10 species: S. normani (Stebbing, 1888); S. biscayensis (Chevreux, 1908); S. talismani (Chevreux, 1919 –1920); S. pirloti (Sheard, 1938); S. laqueus (Barnard, 1967); S. scutatus (Griffiths, 1977); S. mytilus (Barnard & Ingram, 1990); S. carinatus Bellan-Santini, 1997; S. incertus Bellan-Santini, 1997 and S. arabiensis sp. nov.

Remarks. The genus is closely related to Euonyx, which was split by Lowry and Stoddart (1989), into Euonyx and Stephonyx . The key difference between these two genera lies in the mouthparts which are greatly reduced in Euoynx. Euonyx are commensal organisms with specialised mouthparts including maxilla 1 with simple and reduced spine-teeth, a mandible with a reduced incisor, a vestigial lacinia mobilis and no molar (Lowry & Stoddart, 1989). Euonyx contains E. chelatus Norman, 1867, E. coecus Pirlot, 1933 and probably E. cornicus K. H. Barnard, 1925 .