Pertsovius tridentatus

Pertsovius tridentatus gen. et sp. nov.

(Figures 3–4)

Material examined. Holotype: adult female, dissected, total body length 1.00 mm. ZIN accession number 91096. Collected during the R/V “Polarstern” cruise ARK XIV /1a, station 45, Makarov Basin (85° 45’N and 177° 03’E), 18 July 1998, bottom depth 2452 m, depth of collection 2000– 1500 m. Paratype: adult female, dissected, total body length 1.00 mm. ZIN accession number 91097. Collected during the R/V “Polarstern” cruise ARK XIV /1a, station 45, Makarov Basin (85° 45’N and 177° 03’E), 18 July 1998, bottom depth 2452 m, depth of collection 2350– 2000 m.

Species description. Prosome ovoid in dorsal view (Fig. 3: 2), nearly 2.9 times as long as urosome and 2.1 times as long as wide. The first pediger separate from cephalosome, pedigers four and five fused.

Genital double somite almost symmetrical ventrally (Fig. 3: 4), slightly expanding laterally approximately equal in length to two following somites combined. Anterior part of genital double somite protruding ventrally (Fig. 3: 5). Spermathecae visible in ventral view but not obvious when viewed laterally. Anal somite nearly two times longer than preceding somite. Caudal rami slightly asymmetrical, with left ramus slightly longer than right, both bearing four setae.

Antennule of 24 free segments not reaching anal somite (Fig. 3: 3). Mouthparts (Fig. 3: 6–10) relatively well developed compared with other discoid genera, and of typical structure for genus. Maxilliped (Fig. 3: 11) syncoxa with no setae on lobe one.

Р1-Р4 (Figs. 4: 1–5) of typical structure for genus: endopods one-segmented, and exopods three-segmented. Outer spine on first segment of P1 exopod relatively long, but not reaching middle of third segment. Outer spines of second and third segments of exopod approximately equal in length, and almost two times shorter than outer spine on first segment. Outer spine on first exopodal segment of Р2 reaching distal border of second segment. Outer edge of third segment of P2 exopod with three external spines on both legs in holotype and paratype.

Differential diagnosis. In the presence of three external spines on third segment of Р2, P. tridentatus sp. nov. can be distinguished from all other species of this genus.

Etymology. The specific name refers to the number of external spines on the distal segment of P2 exopod.