Euonyx Norman, 1867

Lowry, J. K. & Kilgallen, N. M., 2014, A generic review of the lysianassoid family Uristidae and descriptions of new taxa from Australian waters (Crustacea, Amphipoda, Uristidae), Zootaxa 3867 (1), pp. 1-92 : 18

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

Figures

FIGURE 9. Euonyx chelatus Norman, 1867, A2 from female B, 8.0 mm; MP from female C; all other parts from female A, 6.2 mm; BMNH 1925.9.8:3-7, from North Minch, eastern North Atlantic Ocean. Habitus after Lincoln, 1979. Scale bars: antennae, gnathopods, pereopods, 0.5 mm; remainder, 0.1 mm.