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.

Cyrtonellida is a group of "monoplacophora", representing either a sister taxon to, or a polyphyletic assemblage including, the Trybliida.