This species closely resembles 0. damkaeri, 0. prolata, and 0. walleni, in addition to 0. notopus Giesbrecht, 1891, 1892 (not 1902). Oncaea parila and 0. notopus may be separated from the other three species by P5, with the two terminal setae lengths nearly equal. Oncaea parila may be distinguished from 0. notopus by relative differences in lengths of spines of the endopodites and exopodites of the swimming legs.
Bipolar species. Antarctic (Weddell Sea, Pacific SW), Arctic (Canada Basin), Norwegian Sea, Washington Inland, Sea of Japan
Oceanic, epi- to bathypelagic species
Female:
Endopodite of P4 with subterminal spine half the length of terminal spine and lateral spine longer than P3 terminal spine. P2 and P3 endopodites end in conical projections between the 2nd and terminal spines, P4 without such projection.
Male:
Abdomen about 2.2 times shorter than the cephalothorax. Caudal rami with the dorsal seta slightly longer than the innermost terminal seta and less than half as long as the outer long termainal seta. P2 and P3 endopodites end in conical projections between the 2nd and terminal spines, P4 without such projection. P5 with free segment shorter than that of female, with 2 terminal setae lengths nearly equal.
P6 probably represented by posterolateral flap on ventral surface of genital segment.
Female: 0,61-0,76 mm
Male: 0,49-0,58 mm
