How to recognize an Ischnocalanus female:

Using a binocular :

3 or 4 visible thoracic segments.

Urosome 3 or 4-segmented.

Genital segment longer than the others, protruding in ventral side.

Second urosome segment very short compare to the others.

Furca as long as or shorter than anal segment.

Using a microscope :

P5 uniramous, symmetrical, 3-4 segmented.

Last P5 segment much longer than preceding one.

How to differenciate I. plumulosus from other Ischnocalanus

Using a binocular :

Slender shape (prosome 4x as long as wide).

First segment of A1 carrying a strong, plumose setae.

3 visible thoracic segments.

Urosome 3-segmented.

Furca slightly asymmetrical with a very very long plumose setae on the left (often broken but a strong root is always visible)

Using a microscope :

Posterior border of the genital segment and of the second urosome segment with fine spinules

P5 4-segmented.

First, third and last P5 segment hairy.

Last P5 segment with a long plumose setae, an external spine, an internal setae, and a row of fine spinules (see figure).

Ecological Notes :