Abyssal zones are dark and cold throughout the year. Photosynthetic activity is absent. Deep sea animals are mostly predators and scavengers. The larger forms have wide mouths and huge curved teeth which prevent escape of any prey. Absence of skeleton, flattened bodies are some other characteristics observed. Some also have special structures that produce light on their bellies, around their eyes(which are usually nonfunctional that is, the organisms are blind) and at the sides of their bodies, some animals glow (shows bioluminescence) in the dark waters.