How to recognize an Acartia female:

Using a binocular :

Top of the head quite flat or slightly triangular.

Prosome with a typical slender shape and 4 visible thoracic segments.

A1 longer than the prosome but shorter than the boby, with many quite long and spaced setae.

Urosome 3-segmented.

Furca rather short, approximativelly as long as one urosome segment.

Furcal setae rather robust with a typical fan shape

Tiny P5.

Using a microscope :

No rostrum.

P5 uniramous, 3-segmented, with the last segment modified into a spine.

How to differenciate A. clausi from other Acartia

Using a binocular :

Corners of the last thoracic segment rounded.

Using a microscope :

4-5 very small spines on the corners of the last thoracic segment.

Second segment of P5 as wide as long and bearing a setae as long or slightly longer than the third segment.

Third segment of P5 forming a strong spine 3x as long as the second segment.

Ecological Notes :

Very common. Very abundant in shallow waters.