Oithona similis Claus 1866

The most abundance surface-dwelling copepod of Arctic

Body almost completely transparent, red tinting may be present on female urosome (the tail); Lipid sac can be prominent; Urosome (tail) long (40-50% of prosome); Antennae longer then prosome, but less than total length

Boreal to arctic waters; Bipolar; Abundant on shelves, as well as over deep basins

Females spawn year-round, less in winter; Female carries eggs in 2 elongate clutches until hatching; Clutch size dependent on size of female, with maximums of ~30 and typically ~15-25 eggs; Generation length unclear, suggested as 1 year for Arctic and multiple generations per year in the sub-arctic; Life expectancy uncertain

Microcarnivore feeding on motile phytoplankton and protists, plus copepod nauplii

Can be distinguished from O. atlantica by smaller size, structure of the rostrum and significantly shorter caudal setae.

Cosmopolite, but cold Atlantic waters are preferable locations

Oceanic, epi- to bathypelagic species

Female:
Rostrum is directed down, is only visible from lateral view. Caudal setae are never longer than the abdomen. Eggs inside egg-sac are usually placed in 1 row. Md endopodite with a small seta and 3 setae subequal in length. 2nd endopodal segment of Mx1 present and armed with 1 seta; 1st lobe represented by 1 seta

Male:
Rostrum is absent. Both A1 are geniculate. The caudal setae are significantly shorter than in female.

Female: 0,68-1,20 mm
Male: 0,50-0,82 mm

Arctic to Cape Cod

upper and glacial epipelagic regions of the Gulf and estuary