Sipunculids are worm-like animals with tough elastic
skin that inhabit tubular burrows eroded within coral or free-living in
sand or mud. They have a highly extensible proboscis called the
introvert used to capture organic matter from the water column or to
graze algae from the substrate. The anal opening is located along
its side. Positive identification is based on internal
anatomy. These are preyed upon by fishes and snails and serve as
intermediate hosts to a number of internal parasites.