loriciferans

Loricifera are a phylum of tiny, marine animals that live in sediments. They are distinguished by a lorica, a protective external case formed from plates that encloses the body, and an evertible introvert bearing scalids around the mouth, used for feeding and movement. Adults are typically a few hundred micrometres in length, making them part of the meiofauna.

They occur worldwide in marine sediments, from shallow coastal sands to deep-sea habitats. They live in the interstitial spaces between sediment grains and are usually collected by sediment cores, sieving, or extraction. Their diet consists mainly of microorganisms such as bacteria and unicellular algae, captured with the introvert and processed through the digestive tract.

In classification, Loricifera were described as a distinct phylum in 1983. They are placed within the broader group Scalidophora, a lineage that also includes kinorhynchs and priapulids, and are considered by many researchers to represent a basal lineage within the larger Ecdysozoa, though exact relationships remain subject to debate. Their unique morphology provides important data for understanding early animal evolution and diversification of microscopic marine life.

Life history and biology remain only partially known because loriciferans are small and inhabit sediments. They reproduce sexually, and their development involves larval stages before reaching the adult form, though detailed life cycles vary among species. Overall, loriciferans are a relatively little-studied group whose discovery expanded the known diversity of animal life in marine meiofauna.