Loricifera (lôrˌĭsĭfˈərə) [key], phylum of microscopic animals discovered in 1974. They have spiny heads and unsegmented bodies encased in a vase-shaped anterior that can retract into the posterior trunk. Although research shows that the sexes are separate and they have a large brain, little else is known about them. Because they adhere tightly to the marine gravel or sand in which they live, they are difficult to extract. They hatch as a larval stage, undergo several molts, and reach adult stage. As with the Gnathustomulida, this may account for their late discovery. Locierans appear to be most closely related to the kinorhynchs (Kinorhyncha) and priapulids.