The final chapter describe the different aspect of the reef at night. A fundamental change takes place on the reef at night, as microscopic animals collectively known as zooplankton migrate up from deeper water to feed on the microscopic plants, or phytoplankton, in water shallow enough for them to use the sunlight for photosynthesis. The zooplankton avoid the shallow water in the daytime so that they are less likely to be eaten by reef fish, but at night they rise to feed. Fewer fish are active during the night, as many of them go to sleep in coral crevices, while some that are inactive in the daytime do venture out at night. Other groups of reef creatures hunt or forage at night. Crabs and lobsters that are hidden in the day are out hunting for food. Most echinoderms are also more active at night, such as the basket star ophiuroid, which spreads branching arms to filter plankton from the water. The octopus is also a nocturnal hunter.