Avoidance of predation is of critical importance to any organism, but reef-building organisms might be considered particularly vulnerable due to their immobile, epifaunal life habit. The need for photosymbiotic metazoans to expose large areas of soft tissue to light further increases the risk of predation, as well as fouling. It has been well established that modern coral reefs grow in particular environments where avoidance of, or adaptation to, competition and disturbance are of prime importance (e.g., Connell, 1978; Jackson, 1983; Glynn, 1988). In particular, the control and incidental damage exerted by herbivores, particularly fishes, in limiting the distribution and abundance of algae is probably crucial to the survival of modern coral reefs (e.g., Hay, 1981; Lewis, 1986). As a result, many coral reef organisms are supposed to show a considerable range of anti-predation traits, but unequivocal confirmation of these as adaptations, as well as details of their evolutionary origin and development, remain poorly known.