Most stony corals extend their tentacles to feed on zooplankton, but those with larger polyps take correspondingly larger prey, including various invertebrates and even small fish. In addition to capturing prey in this way, many stony corals also produce mucus films they can move over their bodies using cilia; these trap small organic particles which are then pulled towards and into the mouth. In a few stony corals, this is the primary method of feeding, and the tentacles are reduced or absent, an example being "Acropora acuminata". Caribbean stony corals are generally nocturnal, with the polyps retracting into their skeletons during the day, thus maximising the exposure of the zooxanthallae to the light, but in the Indo-Pacific region, many species feed by day and night.