Ultimachelium nichollsi ( Lowry, 1984 )

Lowry, J. K. & Stoddart, H. E., 2012, The Pachynidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) 3246, Zootaxa 3246 (1), pp. 1-69 : 63

Ultimachelium nichollsi ( Lowry, 1984)

( Figs 44 , 45 )

Pachychelium antarcticum . ― Nicholls, 1938: 14, fig. 3. ― Bellan-Santini, 1972: 215, pl. 28. ― Lowry & Bullock, 1976: 101 (in part). ― Lowry, 1982: 320.

Pachychelium nichollsi Lowry, 1984: 103 . ― Barnard & Karaman, 1991: 510. ― De Broyer & Jazdzewski, 1993: 72.

Ultimachelium nichollsi . ― De Broyer et al., 2007: 158.

Material examined. One ?female, 12 mm, USNM 1156710 , off South Georgia, Southern Ocean, 54°51'S 35°03'W, 168–173 m, trawl, 10 December 1986, Professor Siedlecki, USARP cruise 601, stn 74. –1?male, 10.0 mm, USNM 1157037 , unknown locality, stn AH 4-30. –1?male, 11.5 mm, USNM 1157039 , unknown locality, stn AH 4-40 .

Diagnostic description. Head lateral cephalic lobe large, narrowly rounded; ventral margin subsigmoidal. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum 2-articulate, article 1 long; flagellum with strong callynophore in specimens of unknown sex. Mandible lacinia mobilis absent; lamina dentata absent; accessory setal row absent; molar absent; palp attached distally; palp article 2 broad, as long as article 3; article 3 tapered distally. Maxilla 1 outer plate with 6 setal-teeth in 3/3 arrangement, setal-teeth smooth; palp absent. Maxilliped inner plate absent; outer plate medium size; palp 4-articulate, article 4 large. Gnathopod 1 subchelate; ischium smaller than propodus; merus with anterior margin; carpus extremely compressed; propodus length about 1.9 × breadth, posterior margin extremely reduced, 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 merus without posteroproximal shoulder. Pereopod 6 basis with posteroventral lobe weakly produced; merus longer than broad, without posteroproximal shoulder. Pereopod 7 basis subrectangular, posterodistal corner subquadrate, posterior margin weakly dentate; merus, length of anterior margin 2.6 × proximal breadth. Epimeron 3 posterior margin without projections, posteroventral corner subacute. Uropod 3 biramous, inner ramus just reaching base of article 2 or extending beyond article 1 of outer ramus. Telson slightly shorter than broad, entire.

Remarks. Ultimachelium barnardi and U. nichollsi both have six setal-teeth on the outer plate of maxilla 1 in a 3/3 arrangement. They differ in the shape of mandibular palp article 3 (subparallel sides in U. barnardi , tapering distally in U. nichollsi ); and gnathopod 1 ischium (swollen posteroproximally in U. nichollsi , not swollen in U. barnardi ).

Distribution. South Georgia, Southern Ocean and Adelie Coast, Antarctica; 46–732 m depth.

Figures

FIGURE 44. Ultimachelium nichollsi (Lowry, 1984).?Female, 12.0 mm, USNM 1156710, off Falkland Islands, Southern Ocean.

FIGURE 45. Ultimachelium nichollsi (Lowry, 1984).?Female, 12.0 mm, USNM 1156710, off Falkland Islands, Southern Ocean. Scale for G1 represents 0.5 mm, remainder represent 0.1 mm.