Euomphaloidea
| Euomphaloidea Temporal range: Lower Ordovician–Late Cretaceous |
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| A fossil shell of Euomphalus pentangulatus | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda or ?Monoplacophora |
| Subclass: | Eogastropoda(old taxonomy) |
| Order: | † Euomphalina(old taxonomy) |
| Superfamily: |
† Euomphaloidea de Koninck, 1881 |
Euomphaloidea, originally Euomphalacea, is an extinct superfamily of marine molluscs that lived from the Early Ordovician to the Late Cretaceous, included in the Gastropoda but speculated as instead perhaps Monoplacophora.
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.
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 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 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) 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:
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