Ultimachelium Lowry & Stoddart 2012, gen. nov.

Ultimachelium gen. nov.

Type species. Ultimachelium tac sp. nov.

Etymology. The generic name is contrived.

Diagnostic description. Body shape slender. Head lateral cephalic lobe large, broadly or narrowly rounded. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum article 1 long; flagellum with callynophore in female. Mandible with accessory setal row absent; left lamina dentata absent; palp attached distally; palp article 2 broad, article 3 with subparallel margins or tapered distally. Maxilla 1 outer plate setal-teeth smooth, at least one inner row setal-tooth absent; palp absent. Maxilliped inner plate absent; outer plate medium size; palp 4-articulate, article 4 large. Gnathopod 1 ischium slightly smaller than, subequal to or larger than propodus; corner of palm without robust seta. Gnathopod 2 palm obtuse. Epimeron 3 posteroventral corner projecting, narrowly rounded. Uropod 3 biramous.

Species composition. Ultimachelium contains four species: U. barnardi (Alonso de Pina, 1993); U. nichollsi (Lowry, 1984); U. schellenbergi (Lowry, 1984); U. tac sp. nov.

Remarks. Species in Ultimachelium were previously assigned to Pachychelium. In our view the old concept of Pachychelium is a complex of three genera: Pachychelium in the North Atlantic and North Pacific with one species in the deep-water tropics of north-eastern Australia; Smaraldia, a monotypic genus currently confined to southern temperate Australia; and Ultimachelium in southern South America and the Antarctic.