Jellyfish or sea jellies?
Sometimes referred to as jellyfish, the sea jelly is not a fish at all as it lacks vertebrae.
True sea jellies (or scyphozoans) are single animals that have a bowl or bell-shaped body, fringed with tentacles and oral arms. Largely at the mercy of ocean currents, sea jellies drift in the oceans, feeding on plankton and small fish. There are many different kinds of sea jellies; some more common ones include the moon jelly and spotted jelly.
The box jellies (or cubozoans) are so named due to their square shape when viewed from above. Single tentacles or clusters of tentacles are found on each corner at the base of the cube-shaped bell. Box jellies are unusually strong swimmers and therefore active hunters. The northern Australian stinger, Chironex fleckeri, is one of the deadliest animals in the world!
The bluebottle is a type of hydrozoan, which is not a single animal but a colony of animals that depend on each other for survival. Some animals are specialized for feeding, digestion and reproduction, and one polyp (or animal) produces the gas-filled float. Drifting on the ocean currents, feeding on small fish and other animals, the main tentacle can range up to 10 metres in length.
True sea jellies, box jellies and bluebottles are related to corals and anemones, and are in a group of animals called cnidarians (pronounced nigh-dare-ee-ans). The name comes from the Greek word 'cnidos', meaning sting nettle. A key feature of these animals is the presence of nematocyst or sting cells, found mainly in the tentacles. These specialized stinging cells aid in defence and the capture of prey and can sometimes cause a nasty sting to humans.
To discover more about cnidarians
word fill fact sheet from the Perth Beachcombers Education Kit!For a copy of the Cnidarians: tingly tentacles poster, visit the NMDC Gift Shop and purchase a copy of the January 2008 edition of the Western Fisheries magazine, or contact Western Fisheries at (08) 9203 0353 or email wfsubscriptions@fish.wa.gov.au to subscribe.
