How to recognize a Clausocalanus female:

Using a binocular :

The prosome shape is almost perfectly ovoid.

Only 3 thoracic segments are visible.

A1 as long or slightly longer than prosome.

The rostrum is short and bifurcated.

P5 is small, symmetrical and uniramous.

Urosome has four segments and a regular cylindrical shape.

Furca shorter than preceding segment.

Using a microscope :

P3 Basipod has a calyx like shape (see figures).

P5 is 3-segmented and bifurcated distally.

How to differenciate C. arcuicornis from other Clausocalanus

Using a binocular :

C. arcuicornis is usually bigger than C. paululus , C. pergens and C. furcatus and smaller than C. lividus and C. mastigophorus. However, to differenciate Clausocalanus species the use of a microscope is absolutely necessary.

Using a microscope :

The genital segment is clearly longer than next segment contrary to C. furcatus.

The third segment of P5 is as long as the 2 preceding segments together.

The genital pore has a typical shape (see figures).

Ecological Notes :

Very common all the year long. Maximum abundance in late winter/early spring.

Probably mainly herbivorous.