An extant order of brachiopods that has been an important component of marine benthic communities since the Ordovician. As one of only two Paleozoic orders in the subphylum Rhynchonelliformea that survives to the present, the rhynchonellids exemplify the fate of the Paleozoic evolutionary fauna. Despite their stratigraphic longevity, rhynchonellids have been a remarkably conservative group morphologically.