Orthida

Orthida is an extinct order of articulate brachiopods. Brachiopods are marine invertebrates with two hard shells, or valves, that are superficially similar to bivalve mollusks like clams. Articulate brachiopods are characterized by having a pedicle valve and a brachial valve that are articulated by a hinge with teeth and sockets. The Orthida order flourished during the Cambrian and Ordovician periods, with its peak diversity occurring in the Ordovician. While they were widespread and abundant, their presence declined significantly by the Devonian period, and they eventually became extinct by the end of the Permian period.

Fossils of Orthida are commonly found in marine sedimentary rocks from these ancient time intervals. The shells of orthid brachiopods are typically smooth or have radial costae, which are rib-like ridges. Their internal anatomy, like other articulate brachiopods, included a lophophore, a ciliated feeding organ used to filter food particles from the water. The precise ecological roles and behaviors of Orthida are inferred from their fossil record and the study of modern brachiopods. They likely occupied benthic environments, attaching themselves to the seafloor or to other objects. The extinction of the Orthida, along with many other marine life forms, is often attributed to major extinction events that occurred at the end of the Permian period.