Lower Ordovician (Tremadoc) – Upper Ordovician (Ashgill)
Plectorthidae is an extinct family of stationary, epifaunal suspension feeders.
Description of the Family
- Subcircular to semioval
- Crural fossettes on the teeth supported by variably disposed
- Divergent, bladelike brachiophores
- Curved ventral interarea with variable dorsal interarea
- Quadripartite adductor scars
Treatise on Invertebrate Paleontology, Part H, Vol. 3 (2000):
- Subcircular to transversely semioval plectorthoids commonly with obtuse cardinal extremities, apical plate rarely developed in delthyrium; ventral interarea curved, dorsal interarea variable in length and disposition; teeth with crural fossettes supported by variably disposed plates, ventral muscle field variably cordate but without diductor scars enclosing adductor tracks; brachiophores divergent, bladelike, joined to hinge line by concave fulcra plates and supported by plates convergent on to valve floor, extending forward as variably developed median ridge and containing cardinal process of variable complexity with negligible notothyrial platform; dorsal adductor scars quadripartite, normally with posterior pair larger than anterior.