A phylum of marine, worm-like animals whose common name refers to their horseshoe-shaped, filter-feeding organ (a lophophore). They are sessile suspension-feeders, most living in chitinous burrows. The gut is U-shaped and the anus opens to the exterior on the dorsal surface above the lophophore. Horseshoe worms have a vascular system and blood containing red blood corpuscles containing haemoglobin (a feature that distinguishes them from Bryozoa). It is widely believed that they are ancestral to the Brachiopoda and Bryozoa, although they first appear in rocks of Devonian age (i.e. after the other two phyla). There are two extant genera, with 10 species.
Subjects: Ecology and Conservation — Zoology and Animal Sciences.