Monoplacophora

Monoplacophora is a class of marine molluscs with a single cap-shaped shell and repeated arrangements of several internal organs, including gills, muscles, and nephridia.

Mollusca: Mollusca is a phylum of animals that includes snails, clams, cephalopods, and several smaller groups. Monoplacophora is one of the major living molluscan lineages.
Tryblidium: Tryblidium is an extinct genus of Paleozoic monoplacophorans known from fossil shells. Its fossils document early representatives of the class.
Neopilina galatheae: Neopilina galatheae is a deep-sea monoplacophoran collected by the Galathea expedition in 1952. Its discovery established that monoplacophorans survived beyond the fossil record.
Molluscan phylogeny: Molluscan phylogeny is the reconstruction of evolutionary relationships among molluscs and their ancestors. Monoplacophoran anatomy and fossils are used to test competing reconstructions of molluscan evolution.
Serial homology: Serial homology is the correspondence of repeated structures along an organism's body axis. Repeated organs in monoplacophorans raise questions about whether the structures share a common developmental origin.
Nautiloids: Nautiloids are cephalopod molluscs, living and extinct, with external shells or shell-like internal structures. Their resemblance to some fossil monoplacophorans once complicated interpretation of the fossil record.
Galathea expedition: The Galathea expedition was a Danish deep-sea research voyage conducted from 1950 to 1952. The expedition collected the living monoplacophoran that reshaped the class's study.
Annelida: Annelida is an animal phylum whose members typically have bodies divided into repeated segments. Similar serial repetition in annelids invites comparison, but does not by itself prove close relationship.
Nephridium: A nephridium is an excretory organ that filters or removes waste from an animal's body. Several paired nephridia occur along the monoplacophoran body.
Paleontology: Paleontology is the study of ancient life through fossils and their geological context. Fossils supply most evidence for monoplacophoran history before living species were found.

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