All sipunculids feed through one of three methods: filter feeding, deposit feeding, or by corroding surrounding material, then ingesting it (Cutler, 1994). Studies have shown that their tentacles provide them sufficient sensory information to differentiate between biological food items, and plain sands and grains (Peebles & Fox, 1933). Indeed, the morphology of an individual’s tentacular crown often reflects its feeding method. Sipunculids with no circumoral tentacles, and few small nuchal tentacles – like P. nigrescens – use the third feeding mode. P. nigrescens lives a sedentary adult life. It uses a chelating agent to reduce the pH of the water surrounding coral skeletons to destroy the bonds between corallite wall crystals, then uses the curved hooks and tough epidermal papillae on its introvert to remove the crystals (Williams & Margolis, 1974). Once a coral burrow is created, P. nigrescens collects particulate food available in the surrounding sediment. Generally, it feeds on algae, small invertebrates, detritus and fecal matter, but not many studies have been conducted on their specific prey relationships (Cutler, 1994).