Odontogriphus

Odontogriphus (literally "toothed riddle") is a genus of soft-bodied animals known from middle Cambrian Lagerstätte. Reaching as much as 12.5 centimetres (4.9 in) in length, Odontogriphus is a flat, oval bilaterian which apparently had a single muscular foot, and a "shell" on its back that was moderately rigid but of a material unsuited to fossilization.

Originally it was known from only one specimen, but 189 new finds in the years immediately preceding 2006 made a detailed description possible. (221 specimens of Odontogriphus are known from the Greater Phyllopod bed, where they comprise 0.42% of the community.) As a result Odontogriphus has become prominent in the debate that has gone on since 1990 about the evolutionary origins of molluscs, annelid worms and brachiopods. A group of scientists think that Odontogriphus’s feeding apparatus, which is "nearly identical" to Wiwaxia’s, is an early version of the molluscan radula, a chitinous "tongue" that bears multiple rows of rasping teeth. Hence they classify Odontogriphus and Wiwaxia as close to the ancestors of the first true molluscs. One scientist has presented a different analysis, arguing since 1990 that Wiwaxia is not closely related to molluscs but is much more like a polychaete worm. He argues that the supposed "radula" is nothing of the sort; he classifies Odontogriphus as a basal lophotrochozoan, in other words close to the last common ancestor of molluscs, annelid worms and brachiopods.