Lingulida

Lingulida is an order of inarticulate brachiopods within the phylum Brachiopoda and the class Lingulata. Members have a simple two-valved shell secreted by the mantle, but unlike most brachiopods they lack teeth or sockets in the hinge. The shell is mainly composed of calcium phosphate (apatite) with an organic matrix, making it distinctly phosphatic compared with calcitic shells of many other brachiopods.

Anatomy includes a pedicle used to anchor the animal to soft substrates and a lophophore that protrudes through a gap between the valves for filter feeding. The valves are typically of unequal size, and the hinge lacks a tooth-and-socket mechanism. Lingulids have a long fossil record and retain a generally simple body plan throughout their history.

Fossil evidence places Lingulida in the early Cambrian, and they persist to the present day, making them one of the longest-surviving brachiopod lineages. Their persistence through major Paleozoic and other extinction events has highlighted the conservative morphology of the group. Fossils are globally distributed and commonly found in marine sediments where they inhabited a range of depths and substrate types.

Among living lingulids, Lingula anatina and related species are the best-known representatives. The group's enduring presence and phosphatic shells have made Lingulida a reference point in studies of brachiopod evolution, early marine ecosystems, and biomineralization.