Ascoceratidae is a family of

Ascocerida The Ascocerida are comparatively small, bizarre Orthoceratoids known only from Ordovician and Silurian sediments in Europe and North America, uniquely characterized by a deciduous conch consisting of a longer juvenile portion and an inflated sho ...

, bizarre orthoceratoid

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

s, with longiconic, deciduous early growth stages which undergo period truncation and an inflated breviconic mature ascoceroid stage. The Ascoceratidae are divided into two, unequal subfamilies. Ascoceratinae have an exogastric ascoceroid stage characterized by the development of a protruding neck ending at the aperture, both ocular and hyponomic sinuses which form when fully grown, and

camera A camera is an instrument used to capture and store images and videos, either digitally via an electronic image sensor, or chemically via a light-sensitive material such as photographic film. As a pivotal technology in the fields of photograp ...

e that are mostly confined to the dorsal half of the shell. 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 close to the venter and found only in the adapical portion. Siphuncle segments nummuloidal (beaded in appearance), septal necks cyrtochoanitic (flared outwardly) generally with recumbent (bent back on themselves) brims. The deciduous stage, which is the juvenile or immature, is orthoconic to cytroconic, with long but variable camerae, siphuncle with orthochoanitic septal necks and tubular segments, and generally straight sutures. Ascoceratinae includes the following genera, '' Ascoceras'', '' Aphragmites'', '' Billingsites'', '' Glossoceras'', '' Lindtroemoceras'', '' Parascoceras'', '' Suchertoceras''. With the exception of ''Billingsites'' and ''Suchertoceras'', which are from the Ordovician, these genera are all Silurian. Probillingsitinae, Ascoceratidae in which the mature breviconic portion is globose, with only a short, indistinct apertural neck, obliquely oriented septa and oblique sinuous sutures. The immature deciduous portion is unknown. Probliingsitinae, which is known only from the middle and upper Ordovician was named by Rousseau Flower, 1941, to contain the following two genera. '' Probillingstites'' and what is probably its senior synonym, '' Shamatawaceras''

References

* Rousseau H Flower 1941 Development of the Mixochoanites. Journal of Paleontology, Vol 15, No 5 pp523–548, pls, text-figs, Sept 1941. * W.M Furnish and Brian F Glenister. 1964 Nautiloidea - Ascocerida;

Treatise on Invertebrate Paleontology The ''Treatise on Invertebrate Paleontology,'' published from 1953–2007 by the Geological Society of America and the University of Kansas, then 2009–present by the University of Kansas Paleontological Institute, is a definitive multi-authore ...

Part K, 1964 {{Taxonbar, from=Q4803951 Orthoceratoidea Prehistoric nautiloid families Ordovician cephalopods Silurian cephalopods Middle Ordovician first appearances Silurian extinctions