Box jellyfish box jellyfish's nervous system is more developed than that of many other jellyfish. They possess a nerve ring around the base of the bell that coordinates their pulsing movements, a feature found elsewhere only in the crown jellyfish. Whereas some other jellyfish have simple pigment-cup ocelli, box jellyfish are unique in the possession of true eyes, complete with retinas, corneas and lenses. Their eyes are set in clusters called rhopalia, located in pockets halfway up the outer, flat surfaces of the bell. Each contains two rhopalial ocelli with lenses, one directed upwards and the other downwards and inwards towards the
Helmet jellyfish jellyfish is found in depths up to 7,000 m and is adapted to its dark environment. A weight of up to a ton per square centimeter presses upon the animals, which live in deep sea. At night the helmet jellyfish leaves the depths and swims up toward its food, plankton. With full stomach it turns from the surface back to the depths. Other deep-sea inhabitants feed upon its faeces. Helmet jellyfish reach a body size of up to 30 cm. They consist 90% of water, the rest being tissue and gelatinous mass, which give the animals their form. They light