Featherstar. Close-up of the tentacles of a featherstar. The featherstar is an ancient and primitive echinoderm, a member of the group of invertebrates that includes the starfish. It uses its feathery and fragile arms to catch and convey microscopic plankton and detritus to its mouth, which is located at the base of the arms. Unlike the closely-related sea lily, a featherstar is a free- swimming animal. Photographed off Maratua Island, in the Sulawesi Sea, Indonesia.