Figure 1. Evolutionary relationships among conchiferan molluscs. (a) The common ancestor of cephalopods arose around 530 million years ago (mya). (b) Around 400 mya, the cephalopod lineage split, yielding shelled nautiloids (c) and the soft-bodied coleoids (d). (e) Decapodiform coleoids have 8 arms and 2 tentacles and include cuttlefish, squid, and bobtail squid. (f) Octopuses have 8 arms and completely flexible bodies. Molecular data places the last common ancestor of extant coleoid cephalopods at 270 mya.