Coral-feeding Phestilla lugubris from East Timor

 Dear Brian,
These are the coral-feeding aeolid, Phestilla lugubris. This species feeds on species of Porites coral. Interestingly animals often pair up and form a 'home' spot on the underside of the coral colony they are feeding on, or in a dark crevice, as you describe. Small animals are very difficult to see because the colour of the digestive gland in the cerata is identical to the colour of the region of the coral they are feeding on. Have a look at the coral-feeding Fact Sheet for links to more information on this specialised life style. When I first studied them I wondered if they were solar-powered, like species of Phyllodesmium, but they do not retain the zooxanthellae in their tissues and have no anatomical adaptations to assist in 'farming' zooxanthellae.

The white 'caps' you can see covering the tips of the cerata are interesting because they cover a swollen layer of special sticky glands found in species of Phestilla [see coral-feeding defense]. As its coral food has feeble nematocyts, Phestilla replaces the cnidosac with this thick layer of gland cells.

Best wishes,
Bill Rudman