It is easy to identify the members of a school of true jellyfish (scyphozoa). They are typically thatch or flattened bell shape, covered with upside down short antennae. The mouth of the jellyfish is protruding and hangs like a clapper on its underside. The mouth is split into four lobes, which are equipped with many stinging cells. These cells are designed to paralyze the prey – plankton and fish.
Most jellyfish float in the water like plankton. One of the most common species in the Gulf of Eilat is the Golden Moon jellyfish – Aurelia – which, during the spring season, arrive in Eilat in gigantic swarms, evoking considerable anxiety amongst people bathing in the sea, but this is not justified. The degree of burn from a jellyfish sting is minimal, and it poses no threat to human beings.
The Aurelia reaches up to 40 cm in width, and the tentacles can reach up to the width of the jellyfish in length. Jellyfish have a translucent purple hue. They feed on plankton which is trapped by the saliva excreted from their body. They are gender-assigned organisms (male or female) and their fertilization is internal, with the sperm cells entering through the mouth of the female. The eggs become planula-larvae and these are exited from the body of the female through the mouth. It is possible to see the planula below the body of the transparent bell-shaped jellyfish.
The lifespan of a jellyfish is no more than a year, and a large proportion of them live only a few months.
There is another type of jellyfish which lives here and that is the Cassiopea – ‘Upside Down’ jellyfish, which can reach 12 cm in size. The tentacles are located on the top and it lives inversely from the Aurelia. The Cassiopea lives in shallow water of up to 10 meters, primarily near marine foliage. When it swims, the bell is turned inside out. It does not have a mouth in the center, as does the Aurelia, but has several mouths located on its eight tentacles.
The fertilization season for jellyfish is from April until August. This is the period when their sting is stronger. They are more poisonous than the Aurelia jellyfish and their color derives from the symbiotic algae that are to be found inside the tissue.