Acleistoceras
Encyclopedia
Acleistoceras is a genus of the oncocerid
, nautiloid family Acleistoceratidae
that lived in the shallow seas that covered much of North America during the Devonian
; living from 409—383.7 mya, existing for approximately .
. Sepkoski's listing of Acleistoceras in the Oncoceratida simply follows Flower (1950) and Teichert & Moore (1964).
is subventral, composed of broadly expanded segments which gives it a nummuloidal or beaded appearance.
Oncocerida
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...
, nautiloid family Acleistoceratidae
Acleistoceratidae
The Acleistoceratidae, named by Flower in Flower & Kümmel 1950, is a family of oncocerids that contains genera characterized by depressed exogastric brevicones and cyrtocones that range from the Middle Silurian to the Middle Devonian...
that lived in the shallow seas that covered much of North America during the Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
; living from 409—383.7 mya, existing for approximately .
Taxonomy
Acleistoceras was named by Hyatt (1884) and assigned by Flower (1950) to the newly established Acleistoceratidae which at that time was added to the OncoceratidaOncocerida
The Oncocerida comprise a diverse group of generally small nautiloid cephalopods known from the Middle Ordovician to the Mississippian ,in which the connecting rings are thin and siphuncle segments are variably expanded...
. Sepkoski's listing of Acleistoceras in the Oncoceratida simply follows Flower (1950) and Teichert & Moore (1964).
Morphology
Acleistoceras has a straight to slightly curved breviconic shell (i.e. is short) with a circular to slightly depressed cross section . The maximum diameter is in the forward part of the phragmocone; the body chamber tapers slightly to a transverse, subtriangular aperture with a well-developed hyponomic sinus. The dorsal profile is virtually straight, the ventral profile is convex, giving it an overall exogastric form. The siphuncleSiphuncle
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 Spirula...
is subventral, composed of broadly expanded segments which gives it a nummuloidal or beaded appearance.