lingulids

Lingulids are a group of marine, inarticulate brachiopods in the order Lingulida, within the class Lingulata. They are among the oldest brachiopod lineages, with a fossil record beginning in the Early Cambrian and continuing to the present. The living genus Lingula is the best-known representative, with several species such as Lingula anatina.

Anatomy and shell: Lingulids have two valves that form a simple, hinge-less shell. The shells are typically phosphatic (apatite) and lack the hinge teeth and sockets found in articulate brachiopods. A long, muscular pedicle protrudes from the posterior of the organism and anchors it to soft sediment. Inside, a basic body plan includes a lophophore for feeding, a crown of ciliated tentacles used to filter suspended particles from seawater.

Ecology and behavior: Lingulids are benthic filter feeders that inhabit sandy or muddy substrates in shallow marine settings. They live as free-lying or pedunculated individuals, often partially buried, with the pedicle anchoring them in place. They can tolerate low-oxygen environments and soft sediments, and feed by extending the lophophore to capture particles from the water.

Life history and reproduction: They reproduce sexually, with fertilization typically external and development producing free-swimming larvae that settle to form juveniles.

Fossil record and significance: Lingulids first appear in Cambrian strata and have persisted with relatively little major change, earning them the designation of living fossils. Their long, simple morphology and extensive fossil record make them valuable for studies of brachiopod evolution and paleoenvironments.