Pachychelium Stephensen, 1925

Lowry, J. K. & Stoddart, H. E., 2012, The Pachynidae fam. nov. (Crustacea: Amphipoda: Lysianassoidea) 3246, Zootaxa 3246 (1), pp. 1-69 : 31-32

Pachychelium Stephensen, 1925

Pachychelium Stephensen, 1925: 121 . ― Schellenberg, 1926: 296. ―Schellenberg, 1931: 18. ―K.H. Barnard, 1932: 75. ―J.L. Barnard, 1969a: 354. ― Lowry, 1984: 99. ― Barnard & Karaman, 1991: 509.

Type species. Pachychelium davidis Stephensen, 1925 , by monotypy.

Diagnostic description. Body shape slender. Head lateral cephalic lobe large, narrowly rounded. Antenna 1 peduncular article 1 without posterodistal spine; accessory flagellum article 1 long; [callynophore not known for female]. Mandible with accessory setal row absent; left lamina dentata absent; palp attached distally; palp article 2 broad, article 3 with subparallel margins or distally tapered. 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 3-articulate (article 4 absent). Gnathopod 1 ischium smaller than propodus; corner of palm with simple robust seta or without any robust seta. Gnathopod 2 palm obtuse. Epimeron 3 posteroventral corner broadly rounded. Uropod 3 biramous.

Remarks. With the new species described from the boreal eastern North Pacific and the tropical western South Pacific and the reassignment of some species to Ultimachelium , the distribution of the previously bipolar genus Pachychelium is changed significantly. The sister taxon of Pachychelium appears to be Ultimachelium . The genera differ in the number of articles in the maxillipedal palp (article 4 absent in Pachychelium , large and well developed in Ultimachelium ) and in epimeron 3 which has a broadly rounded posteroventral corner in Pachychelium , projecting and narrowly rounded in Ultimachelium .

Species composition. Pachychelium davidis Stephensen, 1925 ; P. fucaensis sp. nov.; P. tropicalis sp. nov.

Pachychelium antarcticum Schellenberg, 1926 , is regarded as an unidentifiable taxon.