Analysis of drilling predation patterns on the foraminifera of the Galapagos hydrothermal mounds reveals that the predator is highly species-selective in its choice of prey, feeding almost exclusively on the most abundant foraminiferal species, Siphouvigerina auberiana (d'Orbigny). Predation is quite heavy; drillings occur in 27% of the individuals, and most specimens show multiple holes. There are indications that the prey rarely survive attacks. Evidence is presented suggesting predator avoidance behavior in S. auberiana, as well as behavioral countermeasures on the part of the predator. We suggest that the most likely predator is probably the juvenile stage of a naticid gastropod.