Very small copepods with the head and pedigerous segment 1, and pedigerous segments 4 and 5 fused or separated. Female urosome relatively short with 2-4 segments, often 2 setae on the caudal rami much thicker than the others, caudal rami sometimes asymmetrical. Female antenna 1 often much longer than the body and segment 25 is usually long, being at least twice as long as the preceding segment. Male antenna 1 with segments 1-2, 3-6, and 24-25 fused. Basipod 2 of maxilliped with an inner proximal row of conspicuous spines or teeth. Basipod 2 of leg 1 without a seta, there may be fusion between exopod and endopod segments so that in a few species these rami may be both 1-segmented, endopod 2 usually with 4 setae. The outer borders of the distal exopod segments not toothed. Female leg 5 symmetrical, uniramous, of 3 or 4 segments; male leg 5 asymmetrical, uniramous, of 4 segments on the right and 5 segments on the left. (Giesbrecht 1892) A number of features of males and females have not been thoroughly described, presumably because of their small size and the fact that it is difficult to obtain undamaged specimens. Future workers using different methods for capturing these copepods and examining their morphology may find a system for breaking up what is now a long list of described species with a wide variety of combinations of characteristics. Taken from Bradford-Grieve, 1994 (Page 52).