BOREHOLES IN THE MIDDLE DEVONIAN BLASTOID HETEROSCHISMA AND THEIR IMPLICATIONS FOR GASTROPOD DRILLING

Boreholes in over 100 specimens of the Devonian blastoid Heteroschisma and the presence of the gastropod Platyceras (Orthonychia) sp. attach ed to a specimen of Heteroschisma subtruncatus (Hall 1858) suggest tha t platyceratid gastropods were capable of drilling their hosts at leas t as early as the Middle Devonian and thus represent the first known g astropods to have evolved this ability. The presence of similar holes in numerous other Devonian and Mississippian blastoids and the occurre nce of several additional examples of platyceratids attached to blasto ids indicate that the interaction between gastropods and blastoids was not infrequent; as in the case of the gastropod/crinoid interaction, this relationship is interpreted as having been parasitic rather than predatory. The parasitic, drilling platyceratids may have been a facto r in the Paleozoic precursor of the Mesozoic marine revolution: some o f the anti-predatory defenses of crinoids described from the Late Pale ozoic may have been strategies of avoiding platyceratid infestation.