Priapulid Worm

Priapulida, sometimes called penis worms, is a phylum of unsegmented marine worms named for the Greek god of fertility because the shape of their extensible, spiny proboscis resembles a human penis. They live mostly in mud, from comparatively shallow to deep waters, and feed on slow-moving invertebrates such as polychaete worms; some species tolerate hydrogen sulfide, low oxygen and low salinity, and one, Priapulus abyssorum, has been found at depths of 3,000 to 8,000 meters. Twenty-two extant species are known. Molecular and morphological evidence places Priapulida within Ecdysozoa, the group that also includes arthropods and nematodes, with Kinorhyncha and Loricifera as its likely nearest relatives, together forming the proposed clade Scalidophora; priapulid-like fossils date back to at least the Middle Cambrian, when the group was likely a major predator.