Structures and phylogeny of actinoceroid cephalopoda
American Journal of Science 29(169): 1-23
ISSN/ISBN: 0002-9599 Accession: 025534470
A resume in English of a more extensive paper published in German in 1933. A new terminology for the structural features of actinoceroids is proposed, the classification is reviewed and a grouping of the genera into 6 families is given. The morphology of the shell is described in the new terminology, particularly the features of the siphuncle; the most striking element is the complex vascular system in the endo-siphuncle. It is inferred that some of the actinoceroids may have been benthonic in habit; others may have been swimmers. It is also inferred that the actinoceroid animal was rather large before it began to secrete a conch. The older classification based on the size and shape of the septal necks is unsatisfactory; the terms holochoani-tic, orthochoanitic, and cyrtochoanitic are merely descriptive. Endoceroidea replaces largely Holochoanoidea, Actinoceroidea replaces largely Cyrtochoanoidea, Cyrto-ceroidea is used for part of Cyrtochoanoidea, Gompho-ceroidea (provisional) and Nautiloidea, s. s., for part of Orthochoanoidea. A schematic arrangement showing the evolution of the actinoceroids is offered. Bibliography.