Loricifera (from Latin, lorica, corselet + Greek, φορη, phora, bearing) is a small phylum of marine sediment-dwelling animals with twenty-two described species, in eight genera. Aside from these described species, there are approximately 100 more which have been collected and not yet described. They are characterised by a protective outer case called a lorica and their habitat, which is in the spaces between marine gravel to which they attach themselves. The phylum was discovered in 1983 by Reinhardt Kristensen, in Roscoff, France. They are among the very latest of discovered groups of Metazoans. They attach themselves quite firmly to the substratum, and so remained undiscovered for so long. The first specimen was collected in the 1970s, and later described in 1983. They are found at all depths, in different sediment types, and in all latitudes.

The animals have a head, mouth and digestive system as well as a lorica. The armor-like lorica consists of a protective external shell or case of encircling plicae. There is no circulatory system and no endocrine system. Many of the larvae are acoelomate, with some adults being pseudocoelomate, and some remaining acoelomate. The animals are hermaphrodites and probably oviparous. They have a very complex life cycle. The species which live in the deep sea are able to reproduce via parthenogenetic or paedogenetic reproduction. They are not known to be present in the fossil record.

Their closest relatives are thought to be the Kinorhyncha and Priapulida with which they constitute the taxon Scalidophora. The three phyla share four characters in common – chitinous cuticle, rings of scalids on the introvert, flosculi, and two rings of introvert retracts. A group called Introverta is formed with Kinorhyncha, Priapulida, Nematoda, and Nematomorpha.


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