Final answer:
Phoronida, known as horseshoe worms, are named for their lophophore, a horseshoe-shaped set of ciliated feeding tentacles, not to be confused with crustaceans that have horseshoe-shaped shields on their heads.
Step-by-step explanation:
Phoronida are often referred to as horseshoe worms due to their unique anatomy, specifically the shape of their lophophore. The lophophore is a horseshoe-shaped feeding apparatus composed of a set of ciliated tentacles surrounding the mouth used for filter-feeding. Despite the similarity in name, they are not related to small crustaceans that have a head covered by a horseshoe-shaped shield. Phoronids are part of the superphylum Lophotrochozoa which includes organisms having a lophophore for feeding or a trochophore larva for development.
In contrast to the horseshoe worms, phylum Nemertea, for example, has an entirely different feeding mechanism. They possess an eversible proboscis contained within a rhynchocoel to capture food. This proboscis can be extended by hydrostatic pressure to catch prey, and unlike the lophophore, it does not resemble a horseshoe. Though not horseshoe-shaped, it serves a similarly critical role in the animal's survival by facilitating feeding.