Arhynchite hayaoi, family Thalassematidae

Echiuroidea is a phylum of ovoid or bulbous, worm-like marine animals of uncertain affinities, but probably related to the members of the phylum Annelida (the true worms). They differ from annelids by having a single pair of chaetae and by being unsegmented when adult. Echuroids inhabit rock crevices or U-shaped burrows excavated in mud or sand.