Phylogeny and systematics of the Coleoidea

Abstract

Abstract.-The Coleoidea are a monophyletic group of cephalopods characterized by the endocochleate condition of their shell. A phylogeny presented here demonstrates that the Coleoidea comprises three natural groups, ranked as superorders: Belemnoidea Hyatt, Decabrachia Boettger, and Octobrachia Fiorini. The Belemnoidea (belemnites and aulacocerids) contains rostrum-bearing coleoids possessing a closing membrane and multilayered conotheca. The Decabrachia (teuthids and sepiids) is characterized by the possession of ten arms in which the fourth pair is modified as tentacles. The Octobrachia (octopods and vampyromorphs) contains cephalopods in which the ten-armed condition has been modified so that the second arm-pair has been lost or modified. A fourth group, the Phragmoteuthidida, is imperfectly known and may represent a stem group to the Decabrachia and Octobrachia. The systematics of the Coleoidea is revised, and an outline classification of the Coleoidea presented. The systematic status of coleoids from the Devonian Hunriichschiefer (Germany) and Permian Phosphoria Formation (Utah, USA) and the stratigraphical range of the Belemnitida are discussed. Detailed reports of the taxonomic status of the following genera are presented: