Rhynchonellata

Rhynchonellata is a subphylum of brachiopods, a group of marine invertebrates. Brachiopods are bivalved organisms, meaning they possess a shell consisting of two valves, but unlike bivalve mollusks, these valves are dorsal and ventral rather than left and right. The Rhynchonellata subphylum is characterized by a specific internal shell structure and a prominent, often fleshy, pedicle that extends from a hole or groove at the posterior end of the ventral valve. This pedicle is used for attaching the brachiopod to the seafloor.

The shells of rhynchonellates typically exhibit strong plication, or folding, on their surfaces, which can be a distinguishing feature. Internally, the musculature and arrangement of the lophophore, the feeding organ, are also characteristic of this group. Rhynchonellates are exclusively marine and are found in a wide range of habitats, from shallow intertidal zones to deep-sea environments. They are benthic organisms, living attached to substrates like rocks, shells, or sediment.

Fossil evidence indicates that rhynchonellates have a long evolutionary history, appearing in the Ordovician period and persisting to the present day. While the diversity of brachiopods has declined significantly since the Paleozoic era, rhynchonellates remain a relatively common and recognizable component of modern marine faunas. They are important in paleoecological studies due to their widespread distribution and characteristic shell forms.