Clymeniida

Systematic Paleontology Class Cephalopoda Subclass Ammonoidea Order Clymeniida.

The Clymeniida are Late Devonian ammonoids characterized by a dorsal retrochoanitic siphuncle, wherein septal necks point to the rear, toward the apex of the shell. Clymeniid siphuncles, in common with those of the Late Paleozoic Prolecanitida, retain the retrochoanitic aspect the ancestral nautiloids. In individual clymeniids the siphuncle starts off ventral, but quickly in the first few chambers shifts to the dorsal side. There, contituent septal necks may be long, even forming a continuous siphuncular tube.

The forwardly arched septa and goniatitic sutures are ammonoid in nature, and separate the Clymeniida from the ancestral Nautiloidea. Shells are discoidal, wound evolute, some with a wide umbilicus but no umbilical perforation.

Derivation is from the Anarcestidae, possibly from Archoceras, or some similar form.

Four suborders are presently included, the Clymeniina, Cyrtoclymeniina, Gonioclymeniina, and Wocklumariina. This differs from the three superfamilies, Gonioclymeniaceae Hyatt 1884, Clymeniaceae Edwards, 1849, and Parawocklumeriaceae Schindewolf, 1937, found in Part L of the Treatise on Invertebrate Paleontology 1962, resepectively as suborders, Gonioclymeniina, Clymeniina, and Parawocklumeriina.

References Clymeniida in fossilworks A.K. Miller, W.M. Furnish, & O.H. Schindewolf. Paleozoic Ammonoidea. Treatise on Invertebrate Paleontolgy, Part L 1962.