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 :