Arcoscalpellum truncatum (Hoek, 1883)

Figures 1 C, 5

Scalpellum truncatum Hoek, 1883: 92, pl. 6 fig. 13. — Zevina, 1973: 846. Arcoscalpellum truncatum . — Zevina, 1981: 334, fig. 254.

Material examined. NMNS 005087-00073, 1 specimen, Stn. CP185 (22º0.54’N, 119º 27.94’E, 26 Aug. 2002, depth: 2334–2543 m), CL 12.94 mm, CW 7.39 mm, PL 4.06 mm; CEL-BB-46D, 1 specimen, Stn. CP375 (24º16.240’N, 122º11.720’E, 27 Aug. 2006, depth: 2216–2497 m), CL 18.17 mm, CW 9.29 mm, PL 4.39 mm.

Diagnosis. 14 fully calcified capitular plates, white, surfaces striated with radiating lines; tergum pentagonal, bluntly truncated; inframedian latus narrow, triangular, touching upper latus; carinolatus with umbo at basicarinal angle, located in middle of carinal margin; carina bowed, umbo apical.

Description. 14 fully calcified, white plates, surfaces with prominent ridges (Fig. 1 C); tergum pentagonal, bluntly truncated, occludent and basal margins straight, carinal margin slightly convex (Fig. 1 C); scutum with umbo apical, apex projecting over tergum, occludent and basal margins straight, tergal margin slightly concave, occludent and basal margins forming right angle (Fig. 1 C); upper latus trapeziform, carinal margin short, straight (Fig. 1 C); scutal margin long, concave, umbo apical, apex projecting over scutum (Fig. 1 C); rostrolatus quadrangular, scutal and basal margins parallel, umbo at occludent margin of scutum (Fig. 1 C); carinolatus irregular shape, subquadrangular, carinal margin concave, other margins straight, umbo at basicarinal angle, in middle portion of carinal margin, angle not extending beyond carina (Fig. 1 C); rostrum narrow, small (Fig. 1 C). Maxilla triangular, with setae on all margins, maxillary lobe long, naked (Fig. 5 A); cutting edge of maxillule notched, 4 cuspidate setae above notch, notch naked,>7 cuspidate setae below notch (Fig. 5 B); mandible tri-dentate, teeth sharply pointed (Fig. 5 C), lower margin short, with sparse setae, inferior angle setose (Fig. 5 C); mandibular palp elongated triangle, superior margin with sparse setae, denser distally (Fig. 5 D); cirrus I with rami subequal (Fig. 5 F), separated from cirri II–VI; outer ramus longer, slender (10- segmented), inner ramus flattened (8-segmented); cirrus II with outer ramus longer (19-segmented) than inner ramus (14-segmented; Fig. 5 H); cirri III–VI similar, rami long, slender, 28–30 segmented (Fig. 5 E); caudal appendages short, slender, slightly longer than first segment of basal pedicle of cirrus VI, 7-segmented (Fig. 5 G).

Distribution. New Zealand, Australia and Taiwan.

Remarks. This is a new record for Taiwanese waters.