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Loricifera(lôr'ĭsĭf`ərə), 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 GnathustomulidaGnathustomulida
, phylum of microscopic worms described in 1956 that have elongated bodies, cilia, and are hermaphroditic. The 80 known species in this group are geographically widespread; they live mainly in sandy marine sediments, where there is organic material to feed on.
..... Click the link for more information. , this may account for their late discovery. Locierans appear to be most closely related to the kinorhynchs (KinorhynchaKinorhyncha
, phylum containing about 150 species of tiny pseudocoelomate worms, it is widely distributed in marine sediments. The kinorhynch body is divided into 13 segments, each covered with a cuticle and equipped with characteristic spines.
..... Click the link for more information. ) and priapulids.
A phylum of multicellular invertebrates. These marine organisms are entirely meiobenthic; that is, they never exceed a maximum dimension of 400 micrometers and live in sediments ranging from deep-sea red clay to coarse sand or shell hash. They have some of the smallest known cells in the animal kingdom. Although they have been found throughout the world, only 10 species representing three genera and two families have been described. Well over 50 species thought to represent several additional genera are known but remain undescribed.
Adult loriciferans are bilaterally symmetrical. The body is regionated into a mouth cone which telescopically protrudes anteriorly from the center of a spherical, appendage-ringed (up to 400 rings may be present) head; a short, usually plated neck region; and a distinctively loricated (thick-cuticled) thorax-abdomen (see illustration). The head, along with its withdrawn mouth cone, may be inverted into the thorax-abdomen, which is then closed anteriorly by the cuticle of the neck region.
Loriciferans appear to be closely related to the Priapulida and perhaps less so to the Kinorhyncha. Certain structures of the mouth cone suggest affinities to the Tardigrada. Their presence may support the idea that proarthropods could have been developed from aschelminth ancestral stock. See Animal kingdom, Arthropoda, Kinorhyncha, Priapulida, Tardigrada