Spinocalanus antarcticus Wolfenden 1906

S. magnus and S. antarcticus are very close species, but distinguishable from the rest of Spinocalanus. Differences from M. magnus: Females have a stouter and wider cephalothorax, more pronounced asymmetry of the caudal rami, spines on the surface of the 3rd and 4th segments on the endopodite of Mxp and a group of spines on the 3rd segment of the exopodite of P1.

Arctic and Antarctic; typical bipolar species – common and rather abundant in both hemispheres.

Oceanic, mesopelagic species

Deepest occurrence of the adults and youngest copepodites (CI and CII) and shallower occurrence of CIV suggest reproduction at depth and gradual ascent in the course of development from CI to CIV.

Female:
Cephalothorax stout, has a wide oval shape from dorsal view, 2-2.5 times longer than wide. The front end is widely rounded, the back is arched and narrows toward the ventral side. The head and 1st thoracic segment are partially fused, the 4th and 5th thoracic segments separate, the posterior corners of the last are elongate and rounded and reach the middle og the genital segment. Thoracic segments do not carry lateral spines. The cephalothorax is 4.2-5 times longer than the abdomen. The proximal part of the genital segment sometimes carries spines on the back side. The genital segment is as long as wide. The ventral projection is 0.3 as thick as the next abdominal segment. The plate of the genital field has an oval shape, the dorsal side of the spermathecs is inflated, elongate and tilted toward the front of the animal. Caudal rami longer than wide and the left ramus is visibly larger than the left. Caudal chaetae also asymmetrical – the second apical chaeta of the left ramus is the thickest and longest, its length exceeds 6 mm. Inner chaetae are also placed asymmetrically.

A1 longer than the body by 1-3 last segments.
Plate of the Md with a bunch of spines almost to the central of the outer surdace, the feeding edge carries 5 large teeth on its ventral size, 4 narrow teeth on its dorsal side, and a dorsal chaeta.
The gnathobase of Mx1 does not carry a row of chaetae on its front surface. The back surface is covered by scarce small spines.
The proximal part of the outer edge of Mx2 inflated and sometimes covered with spines, the 1st lobe carries 6 chaetae.
The inner edge of the 3rd and 4th segments of the endopodite of Mxp carries a group of spines
The coxopodite of P1 with hairs on the inner edge, the basipodite – with hairs and spines on the inner edge and a transverse row of small spines near the outer edge. All segments of the exopodite of P1 also with a row of small spines near the outer edge.
The surface of the coxopodite of P2-P3 bare, the surface of the coxopodite of P4 with a proximal row of spines and a transverse row of spines near the base of the inner chaeta.
The second segment of the endopodite of P2 with 1 outer chaeta.
The second segment of the exopodite of P2-P4 with a diagonal row of long spines on the dorsal side and a row of spines near the distal end on the ventral side.
The third segment of the exopodite of P2-P3 with a transverse row of stout spines on the dorsal surface, no spines are present on the same segment in P4. The 2nd segment of the endopodite of P3-P4 with 2 rows of spines, the 3rd segment in P3 with 1 row of spines. The same segment in P4 is not armed with spines on its dorsal surface, but the ventral surface carries a row of short spines.

Male:
The posterior corners of the last thoracic segment are practically not elongated, widely rounded. Abdomen is 2.5 times shorter than the cephalothorax. The anal segment is 0.6 times as long as the caudal rami. Caudal rami 1.5 longer than wide, the left ramus is somewhat larger and also carries the longest chaeta.
P5 uniramous and strongly asymmetrical. The right leg reaches the middle of the third abdominal segment and is shorter than the coxopodite of the left leg; the left leg is significantly longer than the abdomen.The third segment carries an apical spine on the right leg, and an inflated proximal part which carries a group of hairs on the left leg.

Female: 2,25-3,15mm
Male: 1,66-2,32 mm

Omnivore/detritovore with a preference for the flux-feeding strategy. Has a looped gut almost 2 times longer than the body (exceptional in free-living copepods)