Pseudactinoceras is an extinct nautiloid cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...

 included in the order Pseudorthocerida

Pseudorthocerida

Pseudorthocerida are generally straight longiconic nautiloids with a subcentral to marginal cyrtochoanitic siphuncle composed of variably expanded segments which may contain internal deposits that may develop into a continuous parietal lining.. Cameral deposits are common and concentrated ventrally...

 and the namesake of the family Pseudactinoceratidae

Pseudactinoceratidae

Pseudactinoceraidae is a family in the nautiloid cephalopod order, Pseudorthocerida, known from the Upper Devonian and Lower Carboniferous ....

(Sweet, 1964).

Description

Pseudactinocras are slightly depressed longiconic cyrtocones with a large siphuncle located between the center and ventral margin. Early siphuncle segments, in the juvenile phragmocone are suborthochoantic; later segments, in the mature phragmocone, become cyrtochoantic, nummuloidal, broader than long. Parietal deposits lining the interior of the siphuncle grow more prominently forward than backward, with canals slightly anterior of segment centers. Thick cameral deposits develop ventrally, but are only thin dorsally (Sweet, 1964).

Taxonomy

Pseudactinoceras was named by Schindewolf in 1943 (Sweet, 1964) and is the type genus of the pseudorthocerid family, Pseudactinoceratidae. The type species, P. promiscuum, came from the Lower Carboniferous (Visean = middle Mississippian) of Germany.