Very clear and practically color-less
Very similar species to M. pusillus some authors argue that it is the same species.
Differences: longer A1, which reach the end of the caudal rami. Narrower third segment of the exopodites of P2, P3 and P4 and narrower and more finely serrated apical spines. The right appendage in P5 in males is equal to 1/2 of the left appendage.
North Pacific, Sea of Japan, Sea of Okhotsk, Bering Sea, all Arctic Seas and Antarctic waters, North Sea, Norwegian Sea
Epi-bathypelagic, occurs at all depths, prefers cold waters. Migrates to greater depths in the winter
Mass reproduction starts before the start of the spring bloom after the vertical migration of adult males and females to the surface. Most likely life cycle takes a year to complete. Reproduction to some extent takes place all year, most likely due to the ability to feed on microzooplankton and detritus.
Microcalanus pusillus G. O. Sars, 1903
Females: Very small copepods with a characteristic, very round and plump, body shape. Maximum width of the cephalothorax is in the top third, slightly narrowed at the head, which has a triangular shape. The corners of the last thoracic segment carry short rounded projections, which are curved at the base. Apical spines of the exopodites of P2, P3 and P4 serrated. A1 reaches the end of the caudal rami. P5 absent.
Characteristic body shape even more pronounced than in females. Head has a triangular shape, rounded projections at the corners of the last thoracic segment are very pronounced. P5 asymmetrical - the left appendage is much larger and composed of 6 segments, the last of which is the smallest. The right appendage is three-segmented, almost half as as long as the left one, the smallest appendage is the third.
Females: 0.60-0.70 mm
Males: 0.70 mm
Morphology of feeding appendages suggests that this species feeds on phytoplankton, as well as microzooplankton and detritus in deep water layers during winter and early spring.