The Nautilida constitute a large and diverse order of generally coiled nautiloid cephalopods that began in the mid Paleozoic and continues to the present with a single family, the Nautilidae which includes two genera, Nautilus and Allonautilus, with six species. All told, between 22 and 34 families and 165 to 184 genera have been recognised, making this the largest order of the subclass Nautiloidea.
The Tarphycerida were the first of the coiled cephalopods, found in marine sediments from the Lower Ordovician to the Middle Devonian. Some, such as Aphetoceras and Estonioceras, are loosely coiled and gyroconic; others, such as Campbelloceras, Tarphyceras, and Trocholites, are tightly coiled, but evolute with all whorls showing. The body chamber of tarphycerids is typically long and tubular, as much as half the length of the containing whorl in most, greater than in the Silurian Ophidioceratidae. The Tarphycerida evolved from the elongated, compressed, exogastric Bassleroceratidae, probably Bassleroceras, around the end of the Gasconadian through forms like Aphetoceras. Close coiling developed rather quickly, and both gyroconic and evolute forms are found in the early middle Canadian.
Bickmorites is an extinct nautiloid cephalopod genus known from the upper Ordovician to the middle Silurian of North America and northern Europe (Norway).
Uranoceras is a barrandeocerid genus from the Middle Silurian belonging to the family Uranoceratidae, characterized by its loosely coiled, gyroconic shell of 1.5 to 2 subquadrate whorls.
Jolietoceras is a compressed, annulate, lituiconic nautiloid included in the derived Tarphycerid family, Uranoceratidae. The shell is gyroconic in the early stage, becoming straight and more rapidly expanded in the later. sutures are straight and transverse. Surface annuli slope strongly to the rear, dorso-ventrally, in the early gyroconic stage but a lacking in the later straight segment.
Laureloceras is a genus of the tarphycerid family Plectoceratidae that lived during the Middle Silurian in what is now North America.
The Barrandeoceratidae is a family of coiled nautiloids included in the Tarphycerida that lived from the Middle Ordovician to the Middle Devonian, characterised by mostly compressed shells with a subcentral siphuncle composed of thin-walled segments that may become secondarily ventral.(Flower and Kummel 1950, Sweet 1964).
The Uranoceratidae is a family of Silurian barrandeoceroids that tend to become uncoiled with age and in which siphuncle segments tend to be expanded into the camerae.
Cummingsoceras is a genus of barrandeoceroids within the Tarphycerida, included in the family Uranoceratidae. Its shell is a rapidly expanding gyrocone of about 1.5 narrowly separated whorls.
Cliftonoceras is a genus of barrandeoceroid type tarphycerids from the Uranoceratidae characterized by a smooth gyroconic shell with a rounded dorsum and flattened venter, and by a subvental siphuncle composed of thin connecting rings and necks that are straight ventrally, recumbent dorsally.
The genus Savageoceras is a barrandeoceratid first known from the Middle Silurian of Illinois consisting of rapidly enlarging, depressed cyrtocones with a trapezoidal section; ventral side wider and flatter than dorsal; sides converging on dorsum. Sutures have slight lateral and ventral lobes and ventrolateral saddles. The surface is covered by transverse striae and has rib-like rings that are more prominent at the ventrolateral shoulders but otherwise vaguely defined. The siphuncle is central; interior unknown.
Lechritrochoceratidae is a family of derived tarphycerids from the middle and upper Silurian, once included in the now largely abandoned Barrandeocerida.
Baeopleuroceras is a genus included in the Barrandeoceroid family Nephriticeratidae, found in Middle Devonian sediments in eastern North America
The Barrandeocerina comprise a suborder of Early Paleozoic nautiloid cephalopods, primitively coiled but later forms may be cyrtoconic, gyroconic, torticonic, and even breviconic, all having empty siphuncles with thin connecting rings. The Barrandeocerina were originally defined as a separate order by Rousseau Flower, but since then have been united within the Tarphycerida as a suborder. Derivation is from the Tarphyceratidae.
Avilionella is a Middle Ordovician tarphyceroid genus consisting of closely coiled, compressed shells with a small perforation in the center, shallow dorsal impression, and subventral tubular siphuncle with thin connecting rings. Chambers are very short, separated by closely spaced, dish-shaped septa. Coiling becomes loose in the mature, adoral, part of the shell.
Chidleyenoceras is a Middle Ordovician tarphyceroid with a closely coiled, evolute shell; whorl section subquadrate, widest just above a broadly rounded venter; dorsum with a broad shallow impression; sutures moderately spaced, weakly sinuous; siphuncle large, subventral, apparently orthochoantitic with tubular segments.
The Apsidoceratidae is a family of Middle and Upper Ordovician Barrandeocerina,, characterized by curved or coiled, smooth, transversely marked, or laterally costate shells, with a conspicuous hyponomic sinus. Early whorl sections tend to be subtriangular; become broader and dorsally impressed in closely coiled forms. Sutures are with lateral lobes in primitive forms but are without lateral lobes, but with ventral lobes in more advanced species with broader sections. Siphuncles are between the center and ventral margin, but not close to either.
Barrandeoceras is a large, coiled, Middle Ordovician nautiloid cephalopod and part of the Tarphycerida. The shell is serpenticonic with whorls touching but not embracing. The adult body chamber becomes freed of the preceding whorl, a rather common character among tarphycerids. Whorl section is oval, somewhat more narrowly rounded ventrally, on the outer rim, than dorsally, on the inner rim. Prominent lateral ribs, at least on inner whorls. Grow lines show a distinct hyponomic sinus. Sutures have lateral lobes. The siphuncle is subcentral.
Plectoceras is a genus of nautiloids included in the tarphycerid suborder Barrandeocerina that lived during the Middle and Late Ordovician. It has been found widespread in the Middle and Upper Ordovician of North America.
Charactoceras is a tarphycerid genus cephalopod which lived during the Late Ordovician.
