Actinocerida

The Actinocerida comprises an order of nauiloid cephalopods with generally straight and slender shells that nearly reach 5 feet (180 cm) in Lower Paleozoic forms but as much as 20 ft in the Upper Paleozoic Rayonnoceras.

Morphologic characters
Actinocerid shells are generally subcircular to eleptical in cross section with subcentral to marginal siphuncles with segments that expand between the septa into the adjacent chambers in most genera. This contrasts with the straight siphuncles of such as the ellesmerocerids and endocerids.

Septal necks, extensions of the septa that form part of the siphuncle, are mostly cyrtochoanitic (outwardly flared), some even recumbant (doubled back). Interiors are filled with secondary deposits which provide added strength and ballasting, through which runs a canal system. This canal system consists of a central canal that runs lengthwise and radial canals that branch off from it at regular intervals. These radial canals connect to a narrow space along the inside of the connection rings known as the parispatium. Cameral deposits are well developed in some, absent in others.

Included Families
The Actinocerida includes the following families;


 * Wutinoceratidae
 * Actinoceratidae
 * Armenoceratidae
 * Ormoceratidae
 * Goniocertidae
 * Lambeoceratidae
 * Huroniidae
 * Carbactinoceratidae