Ulrichoceras
Encyclopedia
Ulrichoceras is recognised as the basal cyrtogomphoceratid genus, which is the source for the rest of the Cyrtogomphoceratidae
as well as for the Westonoceratidae
. The Cyrtogomphoceratidae are endogastric, the Westonoceratidae, exogastric.
Ulrichoceras has a cyrtoconic, endogastric shell that expands fairly rapidly to the middle of the body chamber, then contracts toward the aperture
. The cross section is slightly depressed, atypical for cyrtogomphoceratids but not so for Reudemannoceratids
; dorsal and ventro lateral sides are broadly rounded, the venter moderately flattened. Sutures have broad ventral lobes. The siphuncle
is between the center and the venter; segments are short and not strongly contracted at the septal foremina, connecting rings are thickened and have enlarged bullettes.
Ulrichoceras, named by Foerste, 1925, type U. beloitense, comes from the Middle Ordovician of Wisconsin, U.S.A. It is intermediary in form between Reudemanoceras and the more derived, M -U Ordovican, Strandoceras
.
Cyrtogomphoceratidae
The Cyrtogomphoceratidae is a family in the cephalopod order Discosorida that comprises genera commonly with compressed, endogastrically curved shells. Siphuncles lie close to the venral side, segments are broadly inflated, connecting rings thick and apically expanded thick bullettes. Chambers are...
as well as for the Westonoceratidae
Westonoceratidae
Westonoceratidae are exogastric, mostly compressed, Discosorida of moderate size from the Middle Ordovician to the Lower Silurian.The siphuncle is typically close to the convexly curved outer margin of the phragmocone -the chambered part of the shell- taken to be ventral but may be more central in...
. The Cyrtogomphoceratidae are endogastric, the Westonoceratidae, exogastric.
Ulrichoceras has a cyrtoconic, endogastric shell that expands fairly rapidly to the middle of the body chamber, then contracts toward the aperture
Aperture (mollusc)
The aperture is an opening in certain kinds of mollusc shells: it is the main opening of the shell, where part of the body of the animal emerges for locomotion, feeding, etc....
. The cross section is slightly depressed, atypical for cyrtogomphoceratids but not so for Reudemannoceratids
Reudemannoceratidae
The Reudemannoceratidae are the ancestral and most primitive of the Discosorida, an order of cephalopods from the early Paleozoic. The Reudemannoceratidae produced generally medium sized endogastric and almost straight shells with the siphuncle slightly ventral from the center.-Derivation:The...
; dorsal and ventro lateral sides are broadly rounded, the venter moderately flattened. Sutures have broad ventral lobes. The siphuncle
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 Spirula...
is between the center and the venter; segments are short and not strongly contracted at the septal foremina, connecting rings are thickened and have enlarged bullettes.
Ulrichoceras, named by Foerste, 1925, type U. beloitense, comes from the Middle Ordovician of Wisconsin, U.S.A. It is intermediary in form between Reudemanoceras and the more derived, M -U Ordovican, Strandoceras
Strandoceras
Strandoceras is a stronly curved cyrtogomphoceratid with a laterally compressed cross section from the middle and upper Ordovician of Northern Europe; Estonia, Norway, the U.K....
.