Ultimachelium schellenbergi ( Lowry, 1984 )

Lowry, J. K. & Stoddart, H. E., 2012, The Pachynidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) 3246, Zootaxa 3246 (1), pp. 1-69 : 64-65

Ultimachelium schellenbergi ( Lowry, 1984)

( Fig. 46 )

Pachychelium antarcticum . ―Schellenberg, 1931: 19, fig. 8. ― Lowry & Bullock, 1976: 101 (in part).

? Pachychelium davidis . ―K.H. Barnard, 1932: 75, fig. 32.

Pachychelium schellenbergi Lowry, 1984: 102 , figs 39–41. ― Barnard & Karaman, 1991:550. ― Gonzalez, 1991: 59. ― De Broyer & Jazdzewski, 1993: 74.

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

Material examined. One specimen,?male, 4.8 mm, SMNH no. 116349, Estero Huito, north of Punta Yahuecha , northern part of Golfo de Ancud, Chile, eastern South Pacific Ocean, 41°45'30"S 73°07'50"W, 35 m, dead algae, dredge or trawl, 15 December 1948, Lund University Chile Expedition, stn M18 .

Diagnostic description. Head lateral cephalic lobe large, narrowly rounded; ventral margin curved. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum 2-articulate, article 1 long; flagellum without callynophore in female. 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 5 or 6 setal-teeth in 3/2 or 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 larger than propodus; merus without anterior margin; carpus extremely compressed; propodus length about 1.8 × breadth, posterior margin absent, 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 merus without posteroproximal shoulder. Pereopod 6 basis with posteroventral lobe weakly produced; merus as broad as long, 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 as long as broad, entire.

Remarks. Ultimachelium schellenbergi is a south-western South American species closely related to U. tac . The main difference between these species is the size of the ischium of gnathopod 1, which is larger than the propodus in U. schellenbergi and about the same size as the propodus in U. tac . Ultimachelium schellenbergi is a larger species (about 6 mm) known from shallower water (less than 35 m) than U. tac which is about 3 mm in length and known from depths of 250 to 300 m. Unlike U. schellenbergi , U. tac does not have any slender setae along the anterior margins of pereopods 5 to 7.

Distribution. Southern Chile, eastern South Pacific Ocean; Magellanic area; South Georgia and Falkland Islands, Southern Ocean; 1–35 m depth.

Figures

FIGURE 46. Ultimachelium schellenbergi (Lowry, 1984).?Male, 4.8 mm, SMNH 116349, Golfo de Ancud, Chile. Scales for MX1, 2 represent 0.5 mm, remainder represent 0.1 mm.