Euonyx chelatus Norman, 1867: 202.— Robertson, 1888: 94.— Stebbing, 1888: 673.— Walker, 1889: 77.— Sars, 1891: 117, pl. 40 fig. 1.— Walker, 1892: 244.— Walker, 1895a: 294.— Walker, 1895b: 422.— Norman, 1900: 214.— Scott, 1901: 259.— Stebbing, 1906: 19.— Stephensen, 1923: 41.— Stephensen, 1929: 52, figs 14, 16.—H.B. Moore, 1932: 156.— Stephensen, 1932: 353.— Pirlot, 1933: 120 (key).— Stephensen, 1935: 33.— Moore, 1937: 117.— Jones, 1940: 25, table 1.— Stephensen, 1942: 470 (table).— Jones, 1948: 404.— Enequist, 1949: 387 (table).— Gurjanova, 1951: 159, fig. 34. J.L. Barnard, 1958: 91 (list).— Bruce, Colman & Jones, 1963: 150.— Thurston & Allen, 1969: 358.—Vader, 1978: 127.— Lincoln, 1979: 54, fig. 18.—P.G. Moore, 1984: 32.— Comely & Ansell, 1988: 114, 123.— Costello et al., 1989: 33.— Lowry & Stoddart, 1989: 519.— Barnard & Ingram, 1990: 2 (list), 3 (key).— Barnard & Karaman, 1991: 485.— Palerud & Vader, 1991: 35.— Sainte-Marie, 1991: 217, appendix 1.— Holmes et al., 1997: 186 (list).— Johnson et al., 2001: 198, table 3.— O’Reilly et al., 2001: 36.— Tzvetkova & Golikov, 2001: 88 (table).
? Opis leptochela Bate & Westwood, 1868: 501 fig.
Types. Syntypes: NHM Reg. no. 1911:11:8:13684-13686 (3 specimens, alcohol), 1911:11:8:M843-M845 (3 slides). Type locality. Sleat Sound, Hebrides, North Atlantic Ocean (~ 57°10’N 5°50’W) on the sea urchin Echinus esculentus Linnaeus, 1758.
Habitat. An apparent obligate ectoparasite of the sea urchin Echinus esculentus Linnaeus, 1758 (Vader 1978).
Depth range. 31–900 m (H.B. Moore 1937; Stephensen 1923).
Remarks. There are currently only three recognized species in Euonyx —the type species and the two new species described here. Euonyx chelatus and E. urania show some similarity. Euonyx xarifa is the least similar. It has an apically rounded lateral cephalic lobe (apically acute or subacute in E. chelatus and E. urania); no anterodistal lobe on article 1 of the antenna 1 peduncle (present in E. chelatus and E. urania); mandibular incisor vestigial (reduced in E. chelatus and E. urania); mandibular molar a large flap (absent in E. chelatus and E. urania); lacinia mobilis absent (vestigial in E. chelatus and E. urania); epimeron 3 with a rounded posteroventral corner (forming a spine spine in E. chelatus and E. urania); and the dorsal margin of urosomite 1 forming a rounded boss extending over urosomite 2 (an elongate truncated boss in E. chelatus and E. urania).
Distribution. Northeast Atlantic Ocean. Coasts of Scotland (Norman 1967; Robertson 1888; Scott, 1901); Isle of Man (Bate & Westwood 1868 (as Opis leptochela); H.B. Moore 1937); Norway (Sars 1891); Wales (Walker 1892); England (Walker 1895 a, 1895b); southwest of the Faeroe Islands (Stephensen 1923); west coast of Ireland (Costello et al. 1989); Bay of Biscay (Dauvin & Sorbe 1995). Arctic Ocean. Barents Sea (Sars 1891; Tzvetkova & Golokov 2001).? Northwest Atlantic Ocean. Westof Greenland (determination uncertain) (Stephensen 1923).