BOREHOLE SITE AND PREY SIZE STEREOTYPY IN NATICID PREDATION ON EUSPIRA (LUNATIA) HEROS SAY AND NEVERITA (POLINICES) DUPLICATA SAY FROM THE SOUTHERN NEW-JERSEY COAST

Frequency, size, and site of complete and incomplete boreholes in 225 and 736 empty unbroken shells of the naticids Euspira (Lunatia) heros (Say 1822) and Neverita (Polinices) duplicata (Say 1822), respectively , from the southern New Jersey coast were measured and precisely locat ed on the victim. Cost-benefit curves for each naticid prey species sh ow similar slopes for largest size class of predators (outer borehole diameter = 4.0-6.0 mm). However, size refuge for N. duplicata and E. h eros prey occurred at a whorl diameter (WD) of 52 and 43 mm, respectiv ely. Prey class preferences predicted by cost-benefit analysis are con gruent with actual observed predation mortalities for each prey size c ategory. Cost-benefit analysis also shows that N. duplicata has greate r variability in shell thickness to internal volume ratio within each size (WD) class, a suspected contributing factor to the greater (0.3 v s. 0.1) prey effectiveness of N. duplicata in deterring successful pre dation. Highest frequencies of complete boreholes occur in the first a nd second smallest prey size (WD) classes for N. duplicata, but in the second and third (next to largest) WD classes for E. heros. Outer bor ehole diameter is correlated with WD of prey shells of each naticids s pecies (r = 0.67 and 0.71), an indication of size selective predation. Whorl sector analysis and landmark triangulation shows that both comp lete and most incomplete boreholes are stereotypically located 180-270 degrees counterclockwise from the aperture and nearer the umbilical r egion than the whorl suture. Attempts to drill the umbilical plug of N . duplicata invariably failed.