Jellyfish canal. Cilia in these canals circulate the fluid in a regular direction. The box jellyfish is largely similar in structure. It has a squarish, box-like bell from each of the four lower corners of which hang a short pedalium or stalk which bears one or more long, slender tentacles. The rim of the bell is folded inwards to form a shelf known as a velarium which restricts the bell's aperture and creates a powerful jet when the bell pulsates, allowing box jellyfish to swim faster than true jellyfish. Hydrozoans are also similar, usually with just four tentacles at the edge
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