''Carbactinoceras'' is a genus of Early Carboniferous ( Visean) actincoceroids first found in Europe (Germany) related to '' Rayonnoceras'' but probably smaller.

Description

''Carbactinoceras'' shells are straight and generally unknown beyond the early growth stage. The

siphuncle The siphuncle is a strand of biological tissue, tissue passing longitudinally through the mollusc shell, shell of a cephalopod mollusc. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the li ...

is large, central to subcentral; segments inflated, septal necks cyrochoantiic and recumbent. The endosiphuncular canal system observed is well developed with thin radial canals perpendicular to the central canal, and leading to a narrow seam along the connecting rings called a perispatium.

Taxonomic position

Although ''Carbactinoceras'' had been considered an

actinocerid The Actinocerida are an order of generally straight, medium to large cephalopods that lived during the early and middle Paleozoic, distinguished by a siphuncle composed of expanded segments that extend into the adjacent chambers, in which deposit ...

according to the American Teatise Part K, 1964, based on the internal characters of the siphuncle, the initial chambers of the phragmocone indicate that this genus is an actinoceroid homeomorph (lookalike) belonging phylogenetically to the

Pseudorthocerida Pseudorthocerida is an order of generally straight longiconic (consisting of longicones - long, thin conic shells) orthoceratoids with a subcentral to marginal cyrtochoanitic siphuncle composed of variably expanded segments which may contain in ...

References

* Bjorn Kroger 2007. Carboniferous Actinoceratoid Nautiloidea (Cephalopoda) - a new perspective) . Journal of Paleontology, July 2007 * Curt Teichert, 1964. Actinoceratoidea. Treatise on Invertebrate Paleontology, Part K. Geological Society of America and University of Kansas Press.
''Carbactinoceras''Paleobiology Database
*J.J. Sepkoski 2002. List of Cephalopod genera

Orthoceratoidea Prehistoric nautiloid genera Mississippian cephalopods Carboniferous cephalopods of Europe Carboniferous Germany Fossil taxa described in 1935 Mississippian genera {{paleo-nautiloidea-stub