Differences from similar species M. distinctocephalus:
Female: The lateral spine of the second segment of the exopodite of P1 reaches the base of the lateral spine of the third segment; both spines are narrow and almost equal in length. The distal segments of the exopodite of P1 almost equal in length. The outer spine of the first segment of the exopodite of P2 at least as long as the outer spines of the third segment. Smaller sizes.
Male: The left P5 is longer than the right by the length of the distal segment. The cephalothorax has a “hump” on the dorsal side at the level of the mouth (from side view) and 2 diagonal rows of flat and very fine spines (from dorsal view).
Arctic Basin
Oceanic, meso- to bathypelagic species
Female: Cephalothorax has an elongate-oval shape from dorsal view with a widely rounded front end, which carries 2 dorso-lateral bumps. The head contains lateral projections approximately in the center. When viewed from the side, the cephalothorax has a practically straight back, a smoothly rounded head and a significant widening in the region of the first thoracic segment. The 4th and 5th thoracic segments are separate. The abdomen is 4.5 times shorter than the cephalothorax. The genital segment is 0.6 times as long as wide. The caudal rami are 1.5 times longer than wide. The inner caudal chaeta is rudimentary, shorter than the ramus, plumose. A1 shorter than the body by 4 last abdominal segments. The basipodite and the first segment of the exopodite of P1 with 2-3 small serrations on the distal outer side. The segments of the exopodite are approximately equal in length. P2-P3 have 3-4 small serrations on the distal outer side of the baspodite. The coxopodite (first segment of the protopodite) of P4 with a transverse row of very thin identical spines on the back side; the outer spines of the third segment of the exopodite are finely serrated.
Male: The top of the head with a shallow medial crevice, which is plumose on the edges. From dorsal view, the head has small lateral protrusions approximately in its center. The dorsal side at this level contains 2 diagonal rows of flat and very fine spines. From side view, the back side of the cephalothorax contains a “hump” at the level of the mouth. The 4th and 5th thoracic segments are separate, the posterior corners of the last are slightly elongate and rounded. Cephalothorax is 3.7 times longer than the abdomen. Abdominal segments practically equal in length. Caudal rami 1.3 times longer than wide. A1 longer than the body by 1 last abdominal segment. P5 uniramous, three-segmented; reaches the distal end of the third abdominal segment. The left leg is longer than the right by the length of the distal segment. The segments on the right leg are equal in length, while on the left leg 2>1>3. The first 2 segments of the right leg are almost fused. The inner edge of the third segment of the left leg with long hairs. The distal segment of both legs with a short flattened apical chaeta.
