Notostomata

Notostomata is a historical taxonomic grouping used in paleontology to describe a set of fossil marine invertebrates of uncertain systematic affinity. The term has appeared in older literature as a way to summarize problematic specimens that did not clearly fit established groups.

Throughout its history, Notostomata was variably placed among major invertebrate lineages, with some authors assigning it to echinoderms, others to mollusks or arthropods. Because the material on which it was based is often fragmentary, its membership was unstable and its status as a natural, monophyletic group has been widely questioned.

Notostomatan fossils are represented mainly by isolated hard parts and partial exoskeletons recovered from Paleozoic rocks in various regions. The limited and incomplete nature of the remains makes detailed anatomical reconstruction difficult.

Today Notostomata is generally treated as an historical or ambiguous label rather than a valid clade. Modern authors typically classify its constituent taxa within other, better-supported groups or retain them as incertae sedis.