Rhynchonellate

Rhynchonellate is a term used in paleontology and zoology to describe a group of brachiopods belonging to the order Rhynchonellida. Brachiopods are marine animals that possess a bivalve shell, superficially resembling mollusks like clams. However, brachiopods are not closely related to mollusks and have a distinct internal anatomy and evolutionary history.

Rhynchonellida is characterized by a distinctive internal loop of calcified tissue that supports the lophophore, the feeding organ of brachiopods. This loop is typically convoluted and differs significantly from the loops found in other brachiopod orders. Externally, rhynchonellates are often recognizable by their plicate, or ribbed, shells, although the degree of ribbing can vary. They also generally lack perforations in their shells, unlike some other brachiopod groups.

Fossils of rhynchonellates are common in marine sedimentary rocks from the Devonian period onwards, making them important index fossils for correlating rock layers. They have a long and diverse fossil record, with many extinct species. Living rhynchonellates are found in marine environments worldwide, typically attached to the seafloor. Their classification and evolutionary relationships are subjects of ongoing research within the field of invertebrate paleontology.