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Sars, 1920

Short Description:

Pseudochirella obesa is an aetideid calanoid copepod known after both sexes (female 5.00-6.20 mm and male 5.76 mm in length) from tropical-boreal zone of the World Ocean, mainly mesopelagic.

Taxonomic Description:

Female. Total length 5.00-6.20 mm. Cephalothorax about 4 times longer than abdomen. Th5 posterior corners slightly asymmetrical, rounded, the right one there with knob arranged near ventral side of posterior Th5 corner (lateral view), this part of segment covered with hairs. Genital segment slightly asymmetrical, left side more prominent than right one (dorsal view) and covered with hairs, width of the segment slightly more than length. A1 reaching the end of genital segment. Re1 A2 and Re2 A2 with 1 seta each; Ri1 A2 with 2 setae. Ri1 Md with 2 setae (after Von Vaupel Klein (1984) with 3), Ri2 Md with 9 long terminal setae and 1 short posterior (after Von Vaupel Klein (1984) 2 posterior). Mx1, Mx2 and Mxp typical of the genus. Re P1 3-segmented, separation between Re1 and Re2 incomplete. Ri P2 2-segmented. P4 coxopodite with 7-8 or 7-10 spines.

Male. (Description after Roe (1975) with modifications). Total length 5.76 mm. Cephalothorax about 3 times longer than abdomen. Cephalon and Th1, as well as Th4-Th5 separated. Th5 posterior corners rounded, without spines. A1 21-segmented, reaching Abd3. Oral parts and their setation in comparison with that in female reduced. Re P1 3-segmented, external spine on Re1 P1 small. Ri P2 one-segmented, but line of fusion slightly visible. P4 coxopodite without spines. Left Re2 P5 with 2 teeth in distal part of segment, right Re2 P5 with excavation and rounded projection in proximal part of segment.

Vertical distribution:

Most probably meso-bathypelagic species; found in stratum 700-1250 m (Roe, 1975), once recorded near surface (Markhaseva, 1996), known from total hauls from depths 300-4800 m (Sars, 1925; Jespersen, 1934; Tanaka, 1957b; Grice and Hulsemann, 1967; Bradford and Jillett, 1980; Markhaseva, 1996).

Geographical distribution:

Tropical-boreal species; distributed panoceanic in tropical and subtropical zones of the World Ocean, also found in boreal zone; its northernmost locality: region of the Strait of Davis (Jespersen, 1934), the southernmost region of New Zealand (Bradford and Jillett, 1980); found in the China Sea, the south-eastern and central parts of the Pacific Ocean (Markhaseva, 1996).

Type locality: the north-eastern Atlantic, region of the Bay of Biscay.

Material examined:

3 females from samples: 262, 263, 265. Specimens from the collections of the National Museum of Natural History (Washington, D.C.) were examined. See examined samples module.

Pseudochirella obesa