Because the characters differentiating monoplacophora from cephalopods are few, several monoplacophora have been mistaken for cephalopod ancestors. One such genus is Shelbyoceras, which was reclassified based on a depressed groove that forms a band around the shell, which is similar to a feature seen in Hypseloconus (with whom it might even be synonymous). The septa in this genus are either closely or irregularly spaced.