Chiridiella pacifica is an aetideid calanoid copepod known after both sexes (female 2.50-3.10 mm and male 2.85 mm in length). Species recorded from the north-western part of the Pacific Ocean and in the Indian Ocean and the Sargasso Sea. Mainly bathypelagic species.
Female. Total length 2.50-3.10 mm. Cephalothorax 4-5 times longer than abdomen. Anterior part of lateral skeleton structures of genital field is not wavy. A1 24-segmented, as long as cephalothorax. Ri A2 is about two thirds of Re length; external lobe of Ri2 A2 with 5-6, internal with 6-7 setae, coxo- and basipodite with 1 seta each. Ri2 Md usually with 4 setae. Mx1 gnathobase with 10 setae, second internal lobe reduced; third with 2 (3 after Deevey (1974)), setae, on Ri there are 4, on Re 6-7 setae, external lobe reduced. First and second endites of Mx2 reduced; third one present, but without setae, fourth endite with spines arranged like pincers, fifth endite present as a single curved spine, distal part of Ri Mx2 with 2 setae. Mxp protopodite with 2 setae in distal group, Ri1 Mxp with 3 setae medially, it is 1.5 times longer than protopodite. Re P1 with 1 external spine. P2 with one-segmented (but sometimes with traces of separation) Ri and 3-segmented Re. Re P3-P4 3-segmented; Ri completely or incompletely 3-segmented.
Male. (Description after Deevey (1974) with modifications). Total length 2.85 mm. Md and Mx2 rudimentary. A1 reaching abdomen. Ri A2 slightly longer and wider than Re. Ri2 Md with 8 setae. Mxp and P1 similar to that in females. Ri P2 2-jointed; Ri and Re P3-P4 3-jointed. P4 coxopodite without hairs. P5 biramous, Ri 1-jointed.
Species was found in hauls between 1000 and 3800 m in the Kurile-Kamchatka and Aleutian Trench area (Markhaseva, 1996) and between 1000 and 2000 (mostly between 1500 and 2000 m ) in the Sargasso Sea (Deevey, 1974).
Atlantic Ocean: the Sargasso Sea (Deevey, 1974). Pacific Ocean: the north-western part (Brodsky, 1950; Markhaseva, 1996), regions of the Aleutian, Kurile-Kamchatka and Marianas Trenches, Izu region (Tanaka, 1957). Indian Ocean: in the western part (Markhaseva, 1996).
Type locality: the north-western part of the Pacific Ocean (Brodsky, 1950).
9 females from samples : 21, 63, 86, 96, 139, 196, 201, 395, 401. See examined samples module.
Lectotype: female, N 39813; high latitude expedition of the Arctic Scientific Institution, 25 July 1946; ice-breaker "Severny Polus"; depth of site 4600 m, stratum of sampling: 4000-0 m.