''Paldoceras'' is a genus of
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 ...
s found in the middle
Ordovician of Estonia and Sweden, included in the discosorid family
Apocrinoceratidae
Apocrinoceratidae constitutes a family of Middle Ordovician nautiloid cephalopods characterized by straight or slightly curved, transversely ribbed shells having siphuncles composed of expanded segments, short recurved septal necks, and thick conne ...
. Two species are recognized; ''Paldoceras paldiskense'' found northwest of Paldiski in northern Estonia and ''Paldoceras neptunsakerense'' found on
Ă–land Island, Sweden.
Shells are small, on the order of a few centimeters in length at most, gently expanding and moderately endogastric with the
siphuncle
The siphuncle is a strand of tissue passing longitudinally through the shell of a cephalopod mollusk. Only cephalopods with chambered shells have siphuncles, such as the extinct ammonites and belemnites, and the living nautiluses, cuttlefish, and ...
lying along the inner concave curvature of the shell. Septa are close spaced, less than a millimeter. Siphuncle segments are broadly expanded. Septal necks in ''paldiskense'' are short and generally cyrtochoanitic (flared outwardly). Those in ''neptunsakerense'' are suborthochoanitic. The later ''P. paldiskense'' from 463.5 to ca461 million years ago is also more strongly curved than earlier 472-466 Ma ''P. neptunsakerense''.
References
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''Paldoceras'' on Fossilworks
Prehistoric nautiloid genera
Ordovician animals
Discosorida
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