Acrotretida
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Through Extinction
Many acrotretides have a tall and conical ventral valve with a pedicle opening at the apex, while the dorsal valve is convex to a much lesser degree. Based on preserved muscle scars, the lateral muscles were shifted back and condensed into large bundles of tendons. These replaced the stout, column-like central muscles, which are present in other linguliforms but apparently absent in acrotretides. The larval shell, which is retained near the pedicle opening, has a strongly pitted texture. The adult shell is smooth, with a rounded outline and an organo-phosphatic composition, like other linguliforms.
Subgroups
- Family Acrotretidae Schuchert, 1893 (Lower Cambrian - mid-Silurian [Wenlock])
- Family Biernatidae Holmer, 1989 (Lower Ordovician [Tremadoc] - Middle Devonian)
- Family Ceratretidae Rowell, 1965 (Cambrian)
- Family Curticiidae Walcott & Schuchert, 1908 (Middle Cambrian - Upper Cambrian)
- Family Eoconulidae Rowell, 1965 (Middle Ordovician [Arenig] - Upper Ordovician [Ashgill])
- Family Ephippelasmatidae Rowell, 1965 (Upper Cambrian - Upper Ordovician [Ashgill])
- Family Scaphelasmatidae Rowell, 1965 (Middle Cambrian [Amgan] - Upper Silurian)
- Family Torynelasmatidae Rowell, 1965 (Middle Ordovician [Arenig] - Silurian)
- Incertae sedis genera
- Craniotreta Termier & Monod, 1978
- Dzhagdicus Sobolev, 1992
- Schizotretoides Termier & Monod, 1978
More in Animals
Monotypic taxonTaxonomic group with only one subordinate taxonSpecies descriptionFormal description of a discovered speciesParaphylyType of taxonomic groupIUCN Red ListInventory of the global conservation status of biological speciesSubtropicsGeographic and climate zoneCommon nameName generally used for a taxon, group of taxa or organism(s)