Echinoecus pentagonus lives in association with sea urchins. They can be found on the bases of some urchins, such as the Heterocentrotus mammilatus in the first four photos below, or inside the anus of species such as Echinothrix calamaris. It is possible that our photos include more than one species of crab.
Crabs that live in anus of Echinothrix calamaris, such as the one in the next three photos, generally burst the urchin's balloon-like anal bulb, leaving the crab's rostrum and sometimes its claws visible through the urchin's anal opening. Below a crab is manipulating urchin fecal pellets being deficated in search of edible items.
Created 12 September 2018
Updated 12 August 2022