Actinonaias ligamentina shell description:

“Shell solid, almost regularly long elliptical, rounded in front, rounded slightly or pointed behind about midway up from the base of the shell, young and adult specimens moderately inflated, old specimens decidedly swollen, having a low, rounded posterior ridge, slightly gaping at the anterior base; old shell having a well-developed lunule running through under the beaks; beaks scarcely inflated, low, their sculpture consisting of very faint, doubly-looped, irregular ridges; ligament large, long; surface nearly smooth or marked with rude, irregular, low, concentric ridges, tawny to pale greenish with broad, rather faint and somewhat broken rays; left valve with two small pseudocardinals and two remote, rather small laterals; right valve with two pseudocardinals, the anterior smaller, and sometimes a small posterior third tooth, with one high lateral; beak cavities not deep; muscle scars large, well impressed and smooth; nacre white or pink, much thickened in front in old shells; female shells very slightly produced at posterior base”(Simpson, 2014; Mather, 2007).