Plate 1 issued from : S. Ohtsuka in Publ. Seto Mar. Biol. Lab., 1984, 24 (4/6). [p.360, Fig.1]. Female (from Tanabe Bay, Honshu): 1, habitus (dorsal); 2, idem (lateral left side); 3, forehead (ventral); 4, urosome (dorsal). Nota: Head and 1st pediger separate, 4th and 5th fused. Rostrum strongly develoed, with a pair of long filaments distally and 2 minute hairs proximally. Surface of prosome bearing branching and non-branching hairs. Urosome 4-segmented. Anal segment short with a well-developed operculum. Caudal rami symmetrical (about 1.6 times as long as wide). Right A1 18-segmented. Left A1 16-segmented, much longer than right A1.
Plate 2 issued from : S. Ohtsuka in Publ. Seto Mar. Biol. Lab., 1984, 24 (4/6). [p.361, Fig.2]. Female: 1, left A1; 2, right A1; 3, A2; 4, Md (mandibular blade ); 5, Md (mandibular palp); 6, Mx2; 7, Mxp; 8, P1 (anterior); 9, endopodite of P1 (anterior, all setae omitted); 10, P2 (anterior); 11, P3 (anterior); 12, P4 (posterior); 13, right P5 (terminal segment); 14, left P5 (posterior; terminal segment and basal ones). Nota: Md with heavily chitinized masticatory blade, armed with 4 teeth and 4 minute spinules at the base of the 1st tooth; basipodite of plalpus with 1 inner seta; endopodite wanting; exopodite 3-segmented, bearing 1 seta on segment 1, 1 seta on segment 2, and 2 lateral setae and 1 distal seta on segment 3. Mx2 with 6 inner lobes (endites), 1st with 1 long seta and 2 minute ones, 2nd and 3rd with 2 setae, 4th with 2 spinulose setae, 5th dilated in the middle and having short strong spine with minute spinules along ventral edge of its basal half, 6th bearing a naked seta; endopodite 3-segmented, 1st with 2 serrated setae and 1 serrate strong spine, 2nd with 2 serrated spines, 3rd with 2 serrated spines.
Plate 3 issued from : S. Ohtsuka in Publ. Seto Mar. Biol. Lab., 1984, 24 (4/6). [p.364, Fig.3]. Male: 1, habitus (dorsal); 2, urosome (dorsal; caudal rami omitted); 3, left A1; 4, Mx1; 5, P5 (posterior). Nota: Urosome 5-segmented. Left A1 16-segmented; right A1 18-segmented, shorter than left.
Plate 4 Issued from : M. Chihara & M. Murano in An Illustrated Guide to Marine Plankton in Japan, 1997. [p.724, Pl. 53, fig.56 a-e]. After Ohtsuka, 1984. Female: a, urosome; b, P5; d, habitus (dorsal).
hyperbenthic, coastal.
Observed in west coast of Sicily (Campolmi M., Constanzo G., Crescenti N., and Zagami G. 1999. First record of the hyperbenthic calanoid copepod Metacalanus acutioperculum in the Mediterranean Sea. In, Fourth International Crustacean Congress, July 20-24, 1998, Amsterdam).
For Ohtsuka (1984, p.364) the original description of Metacalanus aurivilli by Cleve (1901) is too incomplete to be compared with the present species, and depends mainly upon the description by Chen & Zhang (1965). M. acutioperculum differs from M. aurivilli in: the smaller numbers of antennular segments; the presence of the apically pointed anal operculum; the more asymmetrical structures of P5 of both sexes; and other details
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