Brodsky, 1950
Short description:
Aetideus pacificus is an aetideid calanoid copepod known after both sexes (female 2.20-2.50 mm and male 1.90-2.10 mm in total length). Species was found in the northern part of the Pacific Ocean usually in epipelagic layers, but also in mesopelagic.
Taxonomic description:
Female. Total length 2.20-2.50 mm. Cephalothorax 3.4 times longer than abdomen. Crest absent. Rostral rami not wide, depth of rostral excavation nearly equal its width. Points of Th5 posterior corners reaching last third of genital segment, not divergent. A1 exceeding caudal rami by last 1-2 segments. Ri2 Md with 11 (9 terminal and 2 posterior) setae. Ri Mx1 with 12 (Park (1968) recorded 15) setae. Ri1 and Mxp protopodite nearly of same length, equipment typical of the genus. Ri P2 2-segmented with incomplete division between segments, all other rami P2-P4 3-segmented. There are about 17 denticles at terminal spines of Re3 P2-P4. There are 4 little spines near the base of internal seta at P4 coxopodite.
Male. Total length 1.90-2.10 mm. Cephalothorax 2.7-3.0 times longer than abdomen. Points of Th5 posterior corners extending the end of first third of Abd2. A1 reaching Abd2. A2 rami about equal in lenght. Caudal rami 3.7 times longer than wide. In comparison to female setation of oral parts reduced. P1-P4 as in female but little spines at P4 coxopodite absent. Width length ratio of second-fourth P5 segments: 1:4.3, 1:8.2 and 1:7.5.
Vertical distribution:
The species is recorded in epipelagic (Park, 1968; Markhaseva, 1996). In the Kurile-Kamchatka Trench area it is found in layers upper than 500 m, usually in 100-200 and 200-500 m, rarely recorded deeper than 500 m down to 1000 m (Markhaseva, 1996).
Geographical distribution:
Pacific Ocean: north-western part, the Sea of Okhotsk, the Bering Sea (Brodsky, 1950); the Kurile-Kamchatka Trench area (Markhaseva, 1996), the north-eastern Pacific (42°N 154°W) (Park, 1968).
Type locality: 43°30'N, 147°30'E (Brodsky, 1950).
Material examined:
Lectotype: female; N 1/39801; Kurile-Sakhalin expedition; August 28, 1948; layer 500-1000 m; depth 1070 m, station 17, sample 88; kept in the Zoological Institute, Russian Academy of Sciences, St. Petersburg.
34 females and 1 male from samples 3, 7, 59, 71, 78, 79, 89, 90, 117, 118, 129-132, 143-145, 153-155, 167-170, 185, 186, 217, 218, 220-224, 227, 238, 248, 249. See examined samples module.