Ammonoids are extinct spiral shelled cephalopods comprising the subclass Ammonoidea. They are more closely related to living coleoids than they are to shelled nautiloids. The earliest ammonoids appeared during the Devonian, with the last species vanishing during or soon after the Cretaceous–Paleogene extinction event. They are often called ammonites, which is most frequently used for members of the order Ammonitida, the only remaining group of ammonoids from the Jurassic up until their extinction.
Euhoplites is an extinct ammonoid cephalopod from the Lower Cretaceous, characterized by strongly ribbed, more or less evolute, compressed to inflated shells with flat or concave ribs, typically with a deep narrow groove running down the middle. In some, ribs seem to zigzag between umbilical tubercles and parallel ventrolateral clavi. In others the ribs are flexuous and curve forward from the umbilical shoulder and lap onto either side of the venter.
The gastropod shell is part of the body of many gastropods, including snails, a kind of mollusc. The shell is an exoskeleton, which protects from predators, mechanical damage, and dehydration, but also serves for muscle attachment and calcium storage. Some gastropods appear shell-less (slugs) but may have a remnant within the mantle, or in some cases the shell is reduced such that the body cannot be retracted within it (semi-slug). Some snails also possess an operculum that seals the opening of the shell, known as the aperture, which provides further protection. The study of mollusc shells is known as conchology. The biological study of gastropods, and other molluscs in general, is malacology. Shell morphology terms vary by species group.
Umbetoceras is an extinct group of marine molluscs. The genus belongs to the goniatitid superfamily Gastrioceratoidea and family Homoceratidae; with examples being found in carboniferous deposits in the Russian Federation and Uzbekistan.
Uraloclymenia is an extinct ammonoid cephalopod genus from the Late Devonian, Famennian stage. The type species is Uraloclymenia volkovi Bogoslovskii, 1977
Brevicoceras is an extinct nautiloid genus from the order Oncocerida with wide distribution in the Middle Devonian in Eastern North America, Russia and Morocco. Nautiloids form a broad group of shelled cephalopods that were once diverse and numerous but are now represented by only a handful of species in two genera.
The Trigonoceratoidea are a superfamily within the Nautilida that ranged from the Devonian to the Triassic, thought to have contained the source for the Nautilaceae in which Nautilus is found.
Syringonautilidae is a family of Nautiloidea from the middle to late Triassic. Syringonautilidae comprise the last of the Trigonoceratoidea and are the source for the Nautilaceae which continued the Nautiloidea through the Mesozoic and into the Cenozoic right down to the recent. Syringonautilidae is a strictly Triassic family, derived early in the Triassic from the Grypoceratidae.
The Centroceratidae is the ancestral family of the Trigonoceratoidea and of the equivalent Centroceratina; extinct shelled cephalopods belonging to the order Nautilida
Protcycloceratidae is an extinct family of slender, commonly annulate, members of the cephalopod order Ellesmerocerida that lived during the Early Ordovician.
Glyphoturris eritima is a species of sea snail, a marine gastropod mollusk in the family Mangeliidae.
Aphelaeceras is an extinct genus from the nautilid family Trigonoceratidae which is part of the Trigonocerataceae, that lived during the Mississippian Period in the late Paleozoic.
Cibolites is a genus of ammonoid in the family Paraceltitidae of the cephalopod order Ceratitida which lived during the Late Permian. The genus was first found the Texas and Mexico. The shell is similar to that of Xenodiscites but smooth and with goniatitic sutures.
Paraceltites is a genus of ammonoid cephalopods in the ceratitid family Paraceltitidae, known from the Middle and Upper Permian of Sicily, the Alps, Crimea, Texas and Mexico. The shell of Paraceltities is evolute with whorls compressed, venter arched and smooth, sides bearing ribs that slant somewhat forward dorso-ventrally. The suture is simple and goniatitic.
Meitianoceras is a genus of ammonites in the ceratitid family Paraceltitidae that lived during the final stage of the Permian, from about 254 to 251 million years ago. The shell of Meitianoceras is small and evolute. All whorls being clearly visible. The outer rim (venter) is angular. The surface of the shell has growth lines or plications. The suture is of the Paraceltites type with 8 unserrated lobes and long, anteriorly, contracted club-shaped external saddles.
Cravevoceras is an Upper Paleozoic ammonite in the goniatite family Cravenoceratidae, probably derived from Pachylyroceras and contemporary with other cravenoceratid genera like Caenolyroceras, Tympanoceras and later Alaoceras and Lyrogoniatites. It is also a member of the Neoglyphioceratoidea.
Biloclymenia is a genus in the ammonoid order Clymeniida which is characterized by a dorsal retrosiphonitic siphuncle with long adapically pointing septal necks.
Darvasiceras was a prolecanitid ammonoid cephalopod from the Early or Lower Permian Chelamchin Formation of Tajikistan. The genus is included in what is now the superfamily Medlicottioidea. The type species is Darvisciceras minum.
Gastrioceras is a goniatitid genus in the family Gastrioceratidae that lived during the late Carboniferous (Pennsylvanian and for most of the Permian.
Eowellerites is genus of ammonoid cephalopods belonging to the Welleritidae family. Species belonging to this genus lived in middle Pennsylvanian (Moscovian). Its fossils were found in USA and Japan. It had thinly discoidal shells with a quite wide umbilicus (U/D = 0.3 - 0.5). While in juvenile stages (up to 15 mm in diameter) venter is moderately rounded, it becomes slightly rounded to flattened when becoming mature (100 mm in diameter). 12-lobed suture has adventitious lobe on the first lateral saddle and is also characterized by an addition of an umbilical lobe. Sutural formula is (V1 V1) L1 L (U1 U2): I D. It has evolved from Winslowoceras henbesti and gave rise to genus Wellerites.
