Euonyx Norman 1867

Euonyx Norman, 1867

(Fig. 9)

Euonyx Norman, 1867: 202.— Sars, 1891: 116.— Stebbing, 1906: 19 (in part). Pirlot, 1936: 116 (in part).—J.L. Barnard, 1969: 342 (in part).— Lincoln, 1979: 54 (in part).— Lowry & Stoddart, 1989: 519.— Barnard & Karaman, 1991: 485, fig. 92I (in part).

Leptochela Boeck, 1876: 190 (homonym, Decapoda) (type species, Opis leptochela Bate & Westwood, 1868, monotypy.

Type species. Euonyx chelatus Norman, 1867, monotypy.

Included species. Euonyx includes four species: E. chelatus Norman, 1867; E. coecus Pirlot, 1933 E. urania sp. nov.; E. xarifa sp. nov.

Incertae sedis. Euonyx conicurus K.H. Barnard, 1955 (genus uncertain);

Diagnostic description. Antenna 1 peduncle article 1 without anterodistal lobe; accessory flagellum with an elongate article 1 (at least twice as long as article 2) partially covering callynophore. Antenna 2 without brush setae. Mandible molar a large, asetose flap or absent. Maxilla 1 outer plate with reduced seta-teeth in a modified 7/4 crown. Maxilla 2 inner plate subequal to or significantly shorter than outer plate. Gnathopod 1 chelate; coxa 1 reduced, significantly shorter than coxa 2, tapering distally or subquadrate; ischium long (length 2 × to 4 × breadth) too very long (length 4 × to 6 × breadth); carpus long (length 2 to 4 × breadth); propodus margins subparallel. Uropod 2 inner ramus not constricted. Telson deeply cleft.

Remarks. Euonyx appears to be the immediate sister taxon of Stephonyx Lowry & Stoddart, 1989. Euonyx has abandoned the scavenging life-style to become an ectoparasite of echinoids and in the process developed severely reduced mouthparts, particularly the seta-teeth of the maxilla 1 outer plate.

In Euonyx coecus Pirlot, 1933 the setal-teeth of maxilla 1 appear to be intermediate between Euonyx and Stephonyx, but the mandibular molar is absent, an important characteristic of Euonyx.

Distribution. North Atlantic Ocean. Indonesia. Eastern Australia.

Key to Euonyx species

1. Antenna 1 peduncular article 1 without anterodistal lobe................................................ E. xarifa - Antenna 1 pedunculararticle 1 withsmalltolargeanterodistallobe ............................................ 2 2. Gnathopod 1 carpus longer than propodus........................................................... E. urania - Gnathopod 1 carpusshorterthanorsubequaltopropodus .................................................... 3 3. Urosomite 1 dorsal margin a broad angled wedge................................................... E. chelatus - Urosomite 1 dorsalmarginanacutetriangularprocess .........................................? Euonyxconicurus - Urosomite 1 dorsalmarginaroundedboss ..................................................... Euonyxcoecus