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An extinct group of epifaunal bivalves that constructed reefs during the late Mesozoic. The valves of rudists are coiled to cylindrical in external form, and the shapes and sizes of rudist shells are extreme relative to other members of the class…

One of the seven existing classes in the phylum Mollusca; sometimes known as Pelecypoda. All members of the Bivalvia (bivalves) are aquatic, living at all depths of the sea and in brackish waters and freshwaters. With about 25,000 living species…

A class of extinct Pelmatozoa in the subphylum Blastozoa which arose in the Ordovician and flourished in the Carboniferous and Permian. Blastoids did not survive the Permo-Triassic mass extinction event. Historically, two orders of the Blastoidea…

A phylum of solitary, exclusively marine, coelomate, bivalved animals, with both valves symmetrical about a median longitudinal plane. Brachiopods are typically attached to the substrate by a posteriorly located cuticle-covered stalk called a…

A phylum of sessile aquatic invertebrates (also called Polyzoa) that form colonies of zooids. Each zooid, in its basic form, has a lophophore of ciliated tentacles situated distally on an introvert, a looped gut with the mouth inside the lophophore…

Part of a clay and silt sequence that accumulated at the foot of a colossal “reef” during the Cambrian explosion, a dramatic evolutionary radiation of animals beginning about 545 million years ago. Although this explosion is most obvious from the…

A class of the phylum Porifera, including exclusively marine sponges with a skeleton composed of spicules of calcium carbonate to which can be added a solid basal calcitic skeleton. The sponges that constitute the phylum Porifera are assigned to…

Primitive fossil members of the phylum Chordata with a calcite skeleton of echinoderm type. They occur in marine rocks of Cambrian to Pennsylvanian age (530–300 million years old) and, because of their skeletons, have traditionally been placed in…

An extinct subclass of stalked Crinoidea; a class of the phylum Echinodermata. The Camerata include more than 235 genera confined to the Paleozoic Era, ranging from the Early Ordovician to the Late Permian. Camerate crinoids were one of the four…

An order of crepuscular (active during predawn or twilight hours) or mainly nocturnal birds collectively known as the nightjars or goatsuckers. Members of the order Caprimulgiformes are apparently most closely related to the owls (Strigiformes).…