Coleoidea

Coleodea, informally coleoids, is a subclass of cephalopods united by the fact of lacking an external shell, thus distinguishing them from nautiloids and ammonoids. Living examples include squids, octopuses, and cuttlefish, which by far dominite the cephalopods of modern seas. The exception is the two nautilid genera Nautilus and Allonautilus.

Coleoids can be subdivided into two major groups, the ancestral Paleocoleoidea and today's living Neocoleoidea. The Neocoleoidea is split into the Decapodiformes and Octopodiformes; the Decapodiformes into  the Myopsoda, Oegopsida, Sepiodea and Spirulida; the Octopodiformes into the Octopoda and Vampyromorpha; and the Octopoda subsequently into the Cirrata and Incirrata.

Decapodiformes have ten appendages, eight arms and two tentacles. The Octopodiformes have only eight arms. Vampyroteuthis, the only living representative of the Vampyromorpha, which has a pair of protractable filaments in addition to its eight arms, is more similar to the cirrate octopods than to any other coleoid.