A LATE PLIOCENE PEA CRAB INFESTATION OF THE SLIPPER-SHELL CREPIDULA FORNICATA (LINNAEUS, 1758) FROM THE YORKTOWN FORMATION OF SOUTHEASTERN VIRGINIA
The presence of this crab in fossil or extant C. fornicata has not been noted before, and the occurrence of pinnotherids in other crepiduloid gastropods are rare.
These minute, free-standing, exceedingly fragile fossil crabs occur in the interior of this fossil Crepidula, one or sometimes 2 per shell, with as many as four per string, in strings of up to 17 shells. Most appear to be immature or first crab-stage females along with a very low incidence of mature females and males. The first Crepidula of each string is often attached to the single valve of a small bivalve, like Spisula, suggesting that these strings were easily transported during severe storms before their apparent rapid burial and death by anoxia and/or starvation. These strings occur in concentrations of more than 50 per cubic decimeter. Preliminary findings suggest that this fossil relationship was much like that between living Z. ostreum and Crassostrea virginica (Gmelin, 1791) where the first crab-stage of this species invades this oyster in mid-summer, a time of potentially severe storms, thus also suggesting that such storms may have migrated along the Eastern United States during a Pliocene summer as well.