A small elongated isopod, which lives in amongst green and brown seaweeds. It can be very hard to find as its colour matches the seaweed exactly. Its maximum length is about 43 mm. Females are wider than males. The trailing edge of the tail is characterised by curving in towards the body and it has two sharp points at either end of the tail fan.

Usually found amongst green seaweed such as sea lettuce or brown seaweed such as zigzag weed, in low intertidal to shallow subtidal. They are not tolerant of freshwater so are not found in estuaries.

This feeds mainly on seaweed.

Mating pairs can often be seen. The male clings to the back of the larger female. She will brood the eggs in a brood pouch holding 10-60 depending upon her size. The eggs hatch into miniatures of the adults and do not disperse over great distances.