Monoplacophora, meaning "bearing one plate", is a polyphyletic superclass of molluscs with a cap-like shell now living at the bottom of the deep sea. Extant representatives were not recognized as such until 1952; previously they were known only from the fossil record, and were thought to have become extinct over 380 million years ago.
The tusk shells or tooth shells, technically the Scaphopoda, are members of a class of shelled marine mollusc with worldwide distribution, and are the only class of exclusively infaunal marine molluscs. Shells of species within this class range from about 0.5 to 15 cm in length. Members of the order Dentaliida tend to be significantly larger than those of the order Gadilida.
Strepsodiscus is an extinct genus of very primitive fossil snail-like molluscs from the early part of the Late Cambrian of North America. The coiled, slightly asymmetrical shells are about 3 cm in height. It is not known whether these are shells of gastropods or monoplacophorans, which are more primitive mollusks.
The Bellerophontidae are an extinct family of specialized globose bellerophontids, Paleozoic and early Triassic mollusks of the class Gastropoda.
Neopilina is a highly derived genus of modern monoplacophoran.
Yochelcionella is an extinct genus of basal molluscs which lived during the Tommotian epoch, the first epoch of the Cambrian period. This genus is often reconstructed to resemble snails.
The molluscshell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.
Helcionelloida is an extinct group of ancient molluscs. These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991.
Micropilina is a genus of monoplacophoran molluscs. They are very small, mostly deepwater animals which have a superficially limpet-like shell.
Bellerophontoidea, common name "bellerophonts", is a superfamily of extinct planospirally-coiled globose molluscs. This superfamily is generally included within the Gastropoda, but may instead be a group of monoplacophorans. The taxon first appeared late in the Cambrian and continued until late in the Triassic.
Stenothecidae is an extinct family of fossil univalved Cambrian molluscs which may be either gastropods or monoplacophorans.
Bucanellidae is an extinct family of Paleozoic molluscs of uncertain position, belonging either to Gastropoda (snails) or Monoplacophora. The family lived from the upper Cambrian to middle Permian and the shells are characterized by a relatively small median sinus in the upper margin of the aperture, and collabral (transverse) or spiral (longitudinal) threads covering the shell. The shells are planispirally coiled rather than trochospirally with a spire as is the case with most shelled gastropods.
The Kirengellids are a group of problematic Cambrian fossil shells of marine organisms. The shells bear a number of paired muscle scars on the inner surface of the valve.
The cephalopods have a long geological history, with the first nautiloids found in late Cambrian strata, and purported stem-group representatives present in the earliest Cambrian lagerstätten.
Tryblidiida is a taxon of monoplacophoran molluscans containing the only extant representatives: 37 species are still alive today, inhabiting the ocean at depths of between 175 and 6,400 metres.
The oesophageal pouches are a pair of pouches connected to the oesophagus of all molluscs, and represent a synapomorphy of the phylum.
Laevipilina is a genus of monoplacophoran molluscs. They are very small, mostly deepwater animals which have a superficially limpet-like shell. All species are at approximately 2–3 mm in length, have 5 pairs of gills, and have 4-5 intestinal coils.
Laevipilina antarctica is a species of monoplacophoran, a superficially limpet-like marine mollusk. It is found in the Weddell Sea and the Lazarev Sea of Antarctica.
Rokopella oligotropha is a species of monoplacophoran, a superficially limpet-like marine mollusc. It is known from only one specimen and a shell fragment collected in the north-central Pacific Ocean.
Vema bacescui is a species of monoplacophoran, a superficially limpet-like marine mollusc.
