Pseudactinoceras
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''Pseudactinoceras'' is an extinct nautiloid
cephalopod A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
included in the order
Pseudorthocerida Pseudorthocerida is an order of generally straight longiconic orthoceratoids with a subcentral to marginal cyrtochoanitic siphuncle composed of variably expanded segments which may contain internal deposits that may develop into a continuous p ...
and the namesake of the family
Pseudactinoceratidae Pseudactinoceraidae is a family in the cephalopod order Pseudorthocerida, known from the Upper Devonian and Lower Carboniferous ( Mississippian).Nautiloidea-Orthocerida by Walter C Sweet, Treatise on Invertebrate Paleontology Part K Mollusca 3, R ...
(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 cyrtochoanitic, 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.


See also

*
List of nautiloids This list of nautiloids is a comprehensive listing of all genera that have ever been included in the subclass Nautiloidea, excluding purely vernacular terms. The list includes all commonly accepted genera, but also genera that are now considered in ...


References

* Sweet, W.C. 1964. Nautiloidea-Orthocerida, Treatise on Invertebrate Paleontology Part K, Mollusca 3; Geological Soc. of America and Univ. Kansas Press.
Paleobiology Database
12/10/09
Sepkoski's Online Genus Database (CEPHALOPODA)
{{Taxonbar, from=Q7254143 Nautiloids Late Devonian first appearances Late Devonian animals Mississippian extinctions