''Robustum nodum'' is the one species of a problematic genus of Ordovician hemithecellid

mollusc Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000 extant species of molluscs are recognized. The number of fossil species is esti ...

proposed by Stinchcomb and Darrough in 1995. Its similarities to ''

Matthevia ''Matthevia'' is a genus of Cambrian molluscs, perhaps related to the chitons. It consists of repeated monoplacophoran-like shells; according to one hypothesis, chitons arose when these tall shells began to overlap over the generations. The tall ...

'' were outlined by Vendrasco & Runnegar.

References

Ordovician molluscs Chitons Fossil taxa described in 1995 Fossils of the United States {{paleo-mollusc-stub