The Barrandeocerina comprise a suborder of Early

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

nautiloid Nautiloids are a group of marine cephalopods ( Mollusca) which originated in the Late Cambrian and are represented today by the living ''Nautilus'' and ''Allonautilus''. Fossil nautiloids are diverse and speciose, with over 2,500 recorded species ...

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, primitively coiled but later forms may be cyrtoconic, gyroconic, torticonic, and even breviconic, all having empty

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 ...

s with thin connecting rings. The Barrandeocerina were originally defined as a separate order by

Rousseau Flower Rousseau Hayner Flower (1913–1988) was an extremely prolific 20th century paleontologist, known for his eccentric personality. Career Although trained as an entomologist, and a specialist in dragonflies and orthopterans, Flower began stud ...

(Flower and Kummel, 1950), but since then have been united within the

Tarphycerida The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician (middle and upper Canad) to the Middle Devonian. Some, such as '' Aphetoceras'' and '' Estonioceras'', are loosely coiled and gyroconi ...

as a suborder (Teichert 1988). Derivation is from the Tarphyceratidae. In early forms the siphuncle is central or subcentral, orthochoanitic (septal necks short and straight), and thin, with tubular segments. Later forms include those with cyrtochoanitic septal necks (curved outward) and segments that may be slightly to strongly expanded into the chambers.

Taxonomy

Six families are included in the Barrandeocerina, (ex Barrandeocerida). : Barrandeoceratidae M Ord-M Dev :

Plectoceratidae The Plectoceratidae is a family of tarphycerids in the suborder Barrandeocerina established as a place for the genus '' Plectoceras''; defined (Sweet 1964) simply as coiled, costate barrandeocerids with subcentral adult siphuncle. According to ...

M-U Ord :

Apsidoceratidae The Apsidoceratidae is a family of Middle and Upper Ordovician Barrandeocerina, (a suborder of tarphycerids), characterized by curved or coiled, smooth, transversely marked, or laterally costate shells, with a conspicuous hyponomic sinus. Early wh ...

M-U Ord : Uranoceratidae U Ord-M Sil : Lechritrochoceratidae M-U Sil : Nephriticeratidae L-M Dev Flower also included the

Lituitidae The Lituitidae are a family of evolved Tarphycerida, tarphycerids characterized by a long orthoconic section that follows a coiled juvenile portion at the apex, along with a generally tubular siphuncle, which like that of the Tarphycerida, barran ...

in the Barrandeocerida, (Flower and Kummel 1950), which were found (Sweet 1964) to have more in common with the Tarphycerida in the original Treatise Part K.

References

*Rousseau H Flower and Bernhard Kummel Jr 1950. A Classification of the Nautiloidea. Journal of Paleontology Vol 24, no.5 pp604–616, Sept 1950 *Walter C Sweet, 1964, Nautiloidea - Barrandeocerida. Treatise on Invertebrate Paleontology Part K Mollusca 3. Geological Society of America and University of Kansas Press *Curt Teichert, 1988. Main Feature of Cephalopod Evolution. The Mollusca Vol.12 Paleontology and Neontology of Cephalopods. Academic Press Prehistoric nautiloids Mollusc suborders Prehistoric animal suborders Taxa named by Rousseau H. Flower {{paleo-nautiloid-stub