Clausocalanus ingens

Zooplankton

Clausocalanus ingens (Frost & Fleminger, 1968)

Small to medium sized copepods
Female rostrum bifurcated
Male rostrum reduced to a knob
Anterior cephalosome and posterior prosome segments are rounded
Cephalosome fused to 1^st pedigerous somite
Female P5 is uniramous, symmetrical and 3-segmented
Male P5 uniramous and of unequal length
Longer P5 nearly always on left, 5-segmented, with segment 5 short and attached sub-apically to the previous segment
Shorter P5 3-segmented, less than half the length of segment 1 of the opposite P5
Female urosome 4-segmented
Can be confused with Paracalanus but the P5 is of a different form

Rostrum in lateral view knob-like and protruding ventrally
Caudal rami less than 1.6x as long as wide
P5 uniramous and of unequal length, longer P5 nearly always on left, 5-segmented, with segment 5 short and attached sub-apically to the previous segment
Shorter P5, 3-segmented, less than half the length of segment 1 of opposite P5

Rostrum in lateral view long, slender and curved ventro-posteriorly
Genital segment more than 1.5x as long as urosome segment 3
Ventral lobe of seminal receptacle small in lateral view, dorsal lobe long and thick
Ventral profile of genital segment non protruberant in lateral view
Females can be identified from other Clausocalanus females in the form of the seminal receptacle in lateral view and the shape of the forehead

(Frost and Fleminger 1968, Nyan Taw 1978, Bradford-Grieve 1994)

Can often be recognised by the blue tint on the cuticle edge of the prosome and pereiopods
Although it is often very abundant in plankton samples little is known about the ecology of this species

Bradford-Grieve, J. M. (1994). The marine fauna of New Zealand: Pelagic Copepoda: Megacalanidae, Calanidae, Paracalanidae, Mecynoceridae, Eucalanidae, Spinocalanidae, Clausocalanidae. National Institute of Water and Atmospheric Research, Wellington, New Zealand.
Frost B. W. & Fleminger, A. 1968. A revision of the genus Clausocalanus (Copepoda: Calanoida) with remarks on distributional patterns in diagnostic characters. Bull. Scripps Inst. Oceanogr. Univ. Calif. 1968;12:1-235.
Taw, N. (1978). Some common components of the zooplankton of the southeastern coastal waters of Tasmania. Papers and Proceedings of the Royal Society of Tasmania 112: 69-136.