Box jellyfish box-like bell, from which its name is derived. From each of the four lower corners of this hangs a short pedalium or stalk which bears one or more long, slender, hollow 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. As a result, box jellyfish can move more rapidly than other jellyfish; speeds of up to per minute have been recorded. In the center of the underside of the bell is a mobile appendage called the manubrium which
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