Ultimachelium tac Lowry & Stoddart 2012, sp. nov.

Ultimachelium tac sp. nov.

(Figs 47, 48)

Ultimachelium tac De Broyer et al., 2007: 158 (nomen nudum).

Type material. HOLOTYPE, male, 3.2 mm, SMNH type no. 8133, east-south-east of Isla Tac, Golfo de Ancud, Chile, eastern South Pacific Ocean, 42°26'40"S 72°59'00"W, 250–300 m, sand and clay with small stones and shell, triangular dredge, 23 January 1949, Lund University Chile Expedition, stn M41A.

Type locality. East-south-east of Isla Tac, Golfo de Ancud, Chile, eastern South Pacific Ocean, 42°26'40"S 72°59'00"W, 250–300 m depth.

Etymology. Named for the type locality; used as a noun in apposition.

Diagnostic description. Head lateral cephalic lobe large, broadly rounded; ventral margin curved. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum 2-articulate, article 1 long; flagellum with strong 2-field callynophore in male, [female not known]. Mandible lacinia mobilis absent; lamina dentata absent; accessory setal row absent; molar absent; palp attached distally; palp article 2 broad, longer than article 3; article 3 tapered distally. Maxilla 1 outer plate with 6 setal-teeth in 4/2 arrangement, setal-teeth smooth; palp absent. Maxilliped inner plate absent; outer plate medium size; palp 4-articulate, article 4 large. Gnathopod 1 subchelate; ischium subequal to propodus; merus without anterior margin; carpus extremely compressed; posterior margin extremely reduced, palm with produced corner, corner of palm without robust seta; dactylus reaching to corner of palm. Gnathopod 2 palm minute, obtuse. Pereonite 4 without dorsal spines. Pereonite 5 without dorsal spines. Pereopod 5 basis subovate; merus without posteroproximal shoulder. Pereopod 6 basis with posteroventral lobe weakly produced; merus longer than broad, without posteroproximal shoulder. Pereopod 7 basis subovate, posterodistal corner rounded , posterior margin weakly dentate; merus, length of anterior margin 1.9 × proximal breadth. Epimeron 3 posterior margin without projections, posteroventral corner subquadrate. Uropod 3 biramous, inner ramus just reaching base of article 2 of outer ramus. Telson slightly longer than broad, entire.

Remarks. Ultimachelium tac has many similarities to U. barnardi but can be separated from that species by the shape of the posteroventral corner of the basis of pereopod 7. See also Remarks under U. schellenbergi.

Distribution. Southern Chile, eastern South Pacific Ocean; 250–300 m depth.