| 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[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]
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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.
In 1952, Raymond Cecil Moore[3] included the Euomphalacea in the gastropod order Archaeogastropoda.
Ponder & Lindberg (1997) and Wagner, again in 2008, included the Euomphaloidea in the order Euomphalina, in turn in the subclass Eogastropoda (revised Prosobranchia), recognising them as valid taxa.
Families in the superfamily Euomphaloidea include:[1]
Boucet and Rocroi (2005)[4] classified Euomphaloidea as Paleozoic molluscs with anisostrophically coiled shells of uncertain position (Gastropoda?). Families in the superfamily Euomphaloidea include:[4]