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Sars, 1902

Short Description:

Chiridius obtusifrons is an aetideid calanoid copepod known after both sexes ( female 4.05-4.60 mm and male 3.10-3.20 mm) and widespread in Arctic Basin, mostly in mesopelagic.

Taxonomic Description:

Female. Total length 4.05-4.60 mm. (Vervoort (1952a) recorded 3.50-4.20 mm). Cephalothorax 2.0-2.9 times longer than abdomen. Posterior points of Th5 corners cover the first third of genital segment, sometimes nearly reaching its middle length. When looking dorsally Th5 corners usually slightly divergent, but sometimes not. Spermatheca significantly smaller than in other species of the genus. Genital segment is the widest in the end of the second and the beginning of its posterior third. A1 slightly longer than cephalothorax. Ri2 Md with 9 setae. Re Mx1 with 10 setae. External spines of Re1 and Re2 P1 exceeding the base of the next spine. Ri P2 one-segmented, not reaching the border between Re2 and Re3 P2. Re P2 indistinctly 3-segmented; first and second external spines on Re3 P2 short and not reaching the base of following spine, terminal spine with 27-31 denticles. P3 and P4 with incompletely 3-segmented rami.

Male. Total length 3.10-3.20 mm. (Vervoort (1952c) recorded 2.90 mm). Cephalothorax 2.6-3.0 times longer than abdomen. Posterior points of Th5 corners slightly not reaching the posterior border of Abd1. A1 about as long as cephalothorax. Ri2 Md with 9 setae. Mx1 with 1-2 setae on the second internal lobe, 3 setae near the base of Ri, 8-9 setae on Ri, 9 setae on Re and 6 setae on external lobe. Ri1 Mxp with 3 medial setae. External spines on Re1 and Re2 P1 shorter than in female, not reaching the base of following spine. P2 with incompletely 3-segmented Re. P3 with indistinctly 3-segmented rami. P4 with 3-segmented rami. Right P5 longer than left.

Vertical distribution:

The species was found in the Arctic Basin in hauls in epi- and mesopelagic (Brodsky and Nikitin, 1955), in the Norwegian Sea in haul 200-800 m (Sars, 1902), and also in significant numbers in total hauls from 2000 m. More common in catches from 350-500 and 600-800 m (Jespersen, 1934) and in 0-50, 50-200 m in the eastern sector of the central part of Arctic Basin (Markhaseva, 1984).

Geographical distribution:

The species is widespread in the Arctic Basin, usually found in its central part. Common in the Strait of Davis, the Norwegian and Greenland seas, was recorded in the Barents Sea (Jespersen, 1934; Vervoort, 1952c; etc), the most southern finding was in the Atlantic Ocean near the coast of North America in the region 42°24'N (Bigelow, 1926). Some findings of the species are very doubtful, but are given here: the Mediterranean Sea (Kovalev and Shmeleva, 1982), near South American coast in the region of 52°53'S (Bjornberg, 1973).

Type locality: Arctic Basin (Sars, 1902).

Material examined:

72 females and 6 males from samples: 471, 472, 475-477, 481, 482, 489, 508, 516, 522, 524, 526, 528, 529, 533, 534, 537, 540-542, 545. See examined samples module.

Chiridius obtusifrons