Although rudists had the "typical" heterodont
crossed lamellar and complex crossed lamellar shell layers (Kennedy and Taylor, 1968), a key synapomorphy for the clade is the possession of an additional outer calcitic shell layer (Skelton and Smith, 2000).
tigerina is heterodont
with two to three wedge-shaped cardinal teeth set in the center near the umbones.
The genus is characterized by a wide, short and flat snout and heterodont
dentition without caniniform teeth.
Spikes" have been reported in other heterodont
bivalves, specifically in the gastrochaenid Spengleria rostrata (Spengler, 1783) by Carter (1978) and more recently in a wide range of veneroids (Glover and Taylor, 2010) and also in their sister group the palaeoheterodonts (Zieritz et al.
Sphaerid and corbiculid clam represent separate heterodont
bivalve radiations into freshwater environments.
Although the Las Hoyas specimens are similar in gross morphology to MIWG2756 and ornithocheirids generally have heterodont
dentitions in terms of tooth size (rather than gross morphology), individual, isolated teeth can only be diagnosed to family level.
Although we don't know how widespread the phenomenon of muscle potentiation is, we do know that it is present in the gills of two other heterodont
bivalves, Mya arenaria and Spisula solidissima.
Owing to the hinge not really being heterodont
, it was transferred to the Palaeoheterodonta Subclass, but its hinge is not as thick and strong as that of the members of the genera in the Unionoidea superfamily bearing cardinal and lateral teeth.