Black sea cucumber

The thick, hard body wall of this black sea cucumber is often covered with sand grains.  One of the larger Hawaiian cucumber species, it often grows to a foot in length. When handled, the body sometimes gives off a red pigment.  Apparently, this chemical is repellant or toxic to predators and may provide protection for the cucumber.  The mouth curves toward the bottom where it scoops up detritus particles and sand with branched feeding tentacles.  After all the organic matter has been digested, the undigested material, mixed with mucus is eliminated in long strands resembling necklaces of sandy beads.  A small black and white spotted crab (Lissocarcinus) is sometimes found living in or around the mouth opening as a commensal.  The crab apparently makes a living feeding from the cucumber’s tentacles and body surface and does not appear to harm its host.  White parasitic snails (Family Eulimidae) may be attached or embedded in the body wall where they feed on the cucumber’s body fluids.