Jellyfish are ancient animals that have been adrift, gliding along in the world seas for more than 500 million years. Carried by waves and sea currents, they are present in all of the world’s oceans, although freshwater species do also exist. These organisms are free- swimming forms of the Medusozoan clade (phylum Cnidaria) with an umbrella-shaped, radially symmetric body plan, representing the adult, sexually mature forms that emerge following the asexual polyp phase, which in turn is sessile, ie. polyps live attached to a substrate. With content of their bodies being up to 98 % water, jellyfish medusae move about aided by the motion of sea water. Virtually all jellyfish feed on plankton and tiny marine animals, which they capture using their tentacles armed with sting cells. These cnidocytes (cells) contain characteristic organelles – ‘cnidae’, which are in fact capsules consisting of a trigger, a spring and a tiny dagger-like sting on top. Upon mechanical or chemical stimulation, a cnida is activated, the prick is thrust forward and a neurotoxin injected into the target organism, thus paralysing it. Nonetheless, jellyfish too have their natural enemies. Namely, certain fish and sea turtle species relish having them on the menu.

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