Early Ordovician – Late Cretaceous
Actinodontida is an extinct order of facultatively mobile infaunal suspension feeders
Characteristics of the Order
- Few teeth, radial and divergent from umbo
- Lateral teeth originate below beak
- Equivalve, with closed margins and, where preserved, prismatonacreous shells; ligament amphidetic or opisthodetic, external and parivincular; dentition generally consisting of few teeth more or less radial and divergent from umbonal region, striated in some genera, rarely becoming taxodont in few genera (uncertain Unionoida); where lateral teeth occur, they originate below beaks and are not separated from cardinals by edentulous interval, as in Heterodonta. [These forms include the actinodonts (earliest known Bivalvia), Trigonioida and Unionoida. They lead in various lines to the Pteriomorphia, Heterodonta, and possibly to the Mytiloida early in the Paleozoic.]
Actinodontoida was named by Douville (1912), was assigned to Palaeoheterodonta by Cope (1997), but was synonymized subjectively with Unionoida by Nevesskaja (2009); it was corrected as Actinodontida by Carter et al. (2011).