North Pacific (coast of Alaska, Aleutian Islands, north of the Bering Sea). May come up to the Arctic through the Bering Strait, occurs in the Beaufort Sea.
Neritic species.
Female:
The ventral surface of the genital segment from lateral view curves immediately posteriad of the genital pore. The genital structures are very similar to that of C. finmarchicus and C. glacialis. The genital plate is smoothly curved in its posterior part and cut-off in the anterior, covering the proximal part of the chitinized seminal receptacles, which are slightly tilted toward the long axis of the body. The posterior corners of the last thoracic segment are always rounded. The additional photoreceptors are much larger than in other Calanus species. Caudal rami are approximately 2 times longer than wide. Mx1 carries spinules proximally on the outer surface. The inner edge of the coxopodite of P5 carries 18-36 serrations (less than in other 2 species), the serrated line is more curved. The medial edge of the basipodite of P5 is more curved than in other 2 species.
Male:
The additional photoreceproeas are much larger than in C. finmarchicus and C. glacialis. The spinifrorm process on the 2nd protopodal segment of P5 and other features same as in female
