Morphological differentiation between species of Pseudocalanus is very ambiguous, identification bordering impossible in juvenile stages. Adult P. mimus most resembles P. minutus in the shape of the cephalosome, but can be distinguished by shorter or absent spiniform processes on the posteroventral margins of the first 2 thoracic segments.
Sea of Japan, Bering Sea, Aleutian Is., Gulf of Alaska, Vancouver Is. Most abundant off the coast of Oregon, Washington
Oceanic, epi-bathypelagic
As differences between species are very subtle, for general morphological description, see genus diagnosis.
Female:
Cephalothorax slender in lateral view, cephalosome somewhat angular, and protruding substantially anteriad of rostrum. The posteroventral margins of the first 2 thoracic segments without, sometimes with small spiniform processes. The posteroventral margin of the 3rd thoracic segment smoothly rounded. The mediodorsal surface of one or more abdominal segments 1-3 with sensillum and integumental pore. Seminal receptacle small. The ratio of the lengths of the 1st and 2nd basipodites of P4 is less than 1.5.
Male:
Prosome slender, anterodorsal sensilla long. Mediodorsal surfaces of urosomal segments 1-3 with sensillum. The ratio of the lengths of the 1st and 2nd basipodites of P4 is less than 1.5. The 2nd abdominal segment is less than 1.37 times longer than the 4th.
