| Euomphaloidea Temporal range: | |
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| A fossil shell of Euomphalus pentangulatus | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| Subclass: | Eogastropoda [1] (old taxonomy) |
| Order: | † Euomphalina [1] (old taxonomy) |
| Superfamily: | † Euomphaloidea de Koninck, 1881 [2] |
Euomphaloidea, originally Euomphalacea, is an extinct superfamily of marine molluscs that lived from the Early Ordovician to the Late Cretaceous, included in the Gastropoda [1] [3] but speculated as instead perhaps Monoplacophora. [4]
Euomphaloid shells are mostly discoidal and may be either orthostrophic (coils wrapped around an erect cone) or hyperstrophic (coils wrapped around an inverted cone); are widely umbilicate and commonly have a channel, presumed exhalent, within the angulation in the outer part of the upper whorl surface. The shell wall is relatively thick, with an external prismatic layer of calcite, which may be pigmented, and an internal layer of lamellar, but not nacreous, aragonite. [5]
As with almost all fossils, the taxonomic relations of and within the euophaloids can only be inferred from their remaining hard parts, in their case the shell. The general inclusion of the Euomphalacea, as originally spelled [3] [5] is based on the asymmetrically coiled tubular shell, suggestive if not indicative of the diagnostic torsion.
J. Brooks Knight, et al, 1960, in the Treatise on Invertebrate Paleontology, Part I, included the Euomphalacea, as then used, in the suborder Macluritina, deriving them from the Macluritacea, and included the following three families.
Prior to, R.C. Moore [3] in 1952, included the Euomphalacea in the gastropod order Archaeogastropoda.
The Euomphaloidea are included in the gastropod order Euomphalina, subclass Eogastropoda (revised Prosobranchia) according to Ponder & Lindberg (1997)Taxonomy of the Gastropoda (Ponder & Lindberg, 1997). This was accepted by Wagner, (2008) [1] revised to include the following families.
In the meantime Boucet and Rocroi (2005)Taxonomy of the Gastropoda (Bouchet & Rocroi, 2005) classified the Eumphaloidea simply as Paleozoic molluscs with anisostrophically coiled shells of uncertain position that are possibly gastropods, recognizing only five families, the:
Prior to being included in the Euomphaloidea, the Anomphalidae, Elasmonematidae, Holopeidae, and Microdomatidae were included in the suborder Trochina, Cox & Knight 1960; the Anomphalidae in the Anomphalacea, the Elasmonematidae and Microdomatidae in the Microdomatacea, and the Holopeidae in the Plytyceratacea. The Raphystomatidae were included in the Pleurotomaracea, Pleurotomarina.
Omphalocirrus is included in the Maclurridae in the Treatise, 1960, [5] but Lioomphalus, given as also in the Omphalocerridae [6] is a synonym for Euomphalus , Euomphalidae,
Caenogastropoda is a taxonomic subclass of molluscs in the class Gastropoda. It is a large diverse group which are mostly sea snails and other marine gastropod mollusks, but also includes some freshwater snails and some land snails. The subclass is the most diverse and ecologically successful of the gastropods.
Bellerophon is a genus of extinct paleozoic marine molluscs of uncertain position in the family Bellerophontidae.
Strepsodiscus is an extinct genus of very primitive fossil snail-like molluscs from the early part of the Late Cambrian of North America. The coiled, slightly asymmetrical shells are about 3 cm in height. It is not known whether these are shells of gastropods or monoplacophorans, which are more primitive mollusks.
The Bellerophontida is a taxonomic order of extinct marine mollusks that are found in the fossil record from the Lower Cambrian to the Lower Triassic. They are considered by some experts to be primitive sea snails with primarily symmetrically coiled shells, marine gastropod mollusks.
The Bellerophontidae are an extinct family of specialized globose bellerophontids, Paleozoic and early Triassic mollusks of the class Gastropoda.
The Euomphalina comprise a major suborder of mainly Paleozoic archaeogastropods, shells of which are hyperstophic to depressed orthstrophic, commonly with an angulation at the outer upper whorl surface thought to be coincident with the exhalent channel; shell wall thick, outer layer calcitic, inner layers aragonitic but not nacreous; operculum calcareous and heavy. Their range is from the Upper Cambrian to the Triassic, and possibly as high as the Upper Cretaceous.
Helcionelloida is an extinct group of ancient molluscs. These are the oldest known conchiferan molluscs, that is, they had a mineralised shell. Some members of this class were mistaken for Monoplacophorans. The class was erected by Peel in 1991.
The taxonomy of the Gastropoda, as revised by Winston Ponder and David R. Lindberg in 1997, is an older taxonomy of the class Gastropoda, the class of molluscs consisting of all snails and slugs. The full name of the work in which this taxonomy was published is Towards a phylogeny of gastropod molluscs: an analysis using morphological characters.
Bellerophontoidea, common name "bellerophonts", is a superfamily of extinct planospirally-coiled globose molluscs. This superfamily is generally included within the Gastropoda, but may instead be a group of monoplacophorans. The taxon first appeared late in the Cambrian and continued until late in the Triassic.
Euomphalidae is an extinct family of Paleozoic to early Mesozoic marine molluscs which may be gastropods with anisostrophically coiled shells . The shells show a selenizone.
Bucanellidae is an extinct family of Paleozoic molluscs of uncertain position, belonging either to Gastropoda (snails) or Monoplacophora. The family lived from the upper Cambrian to middle Permian and the shells are characterized by a relatively small median sinus in the upper margin of the aperture, and collabral (transverse) or spiral (longitudinal) threads covering the shell. The shells are planispirally coiled rather than trochospirally with a spire as is the case with most shelled gastropods.
Bucaniidae is an extinct family of Paleozoic molluscs of uncertain position possibly being either gastropods or monoplacophorans in the superfamily Bellerophontoidea. The family lived from the Lower Ordovician to the Devonian and have shells in which the apertural margins tend to flare. Most genera have a slit and selenizone, others some modification of this feature.
Euphemitidae is an extinct family of Paleozoic fossil molluscs of uncertain position. They have isostrophically coiled shells and may be either Gastropoda sea (snail)s, or Monoplacophora.
Macluritidae is an extinct family of relatively large, Lower Ordovician to Devonian, macluritacean gastropods(?), hypserstrophically coiled, that is dextral while appearing sinistral, of which the genus Maclurites is arch-typical. The base of their shells is flat or gently protruding while the upper side is generally concave.
Omphalotrochidae is an extinct taxonomic family of Paleozoic molluscs (gastropods?) with anisostrophically coiled shells of uncertain position (Gastropoda?).
Omphalocirridae is an extinct family of Paleozoic molluscs (gastropods?) with anisostrophically coiled shells of uncertain position (Gastropoda?).
Helicotomidae is an extinct family of Paleozoic molluscs (gastropods?) with anisostrophically coiled shells of uncertain position (Gastropoda?).
The Anomphalidae is an extinct family of fossil sea snails, marine gastropod mollusks. These are archaeogastropods which are included in the suborder Trochina. The Anomphalidae lived during the Paleozoic, from the Silurian to the Middle Permian. According to some authorities these snails belong instead to the Euomphalacea.
The †Raphistomatidae is a taxonomic family of fossil sea snails, Paleozoic marine gastropod molluscs. This family was established by Koken in 1896. This family is found in the fossil record from the Upper Cambrian to the Middle Permian.
The Trochina is a taxon that is used by paleontologists. It is a suborder of primitive sea snails, marine gastropod mollusks.