has a smooth, flattened saucer-shaped bell (the umbrella) with eight simple marginal lobes. The umbrella is colourless, while the radial canals, oral arms and gonads are typically mauve, violet, reddish, pink or yellowish in colour. Aurelia aurita
usually grows to approximately 25 cm in diameter but can reach 40 cm. The umbrella is quite thick, thinning towards the edge, with numerous short, hollow tentacles forming a fringe around the edge. These short tentacles are ringed by numerous stinging cells (nematocysts). There are four interfolded gonads that form a horseshoe or near circle shape in the centre of the umbrella. Eight branched and eight un-branched canals connect to the marginal ring-canal of the umbrella. The mouth is formed on a projection on the underside of the umbrella (the manubrium). Four thickened oral arms, each with a central groove, edged by thinner folded lips and lined with small tentacle-like processes approximately 2 mm long. The surface of the oral arms is covered with nematocysts, crowded together near the tips of the tentacles. The oral arms are slightly shorter than the radius of the umbrella. The stomach consists of four circular shaped interradial gastric pouches connected to the mouth by grooves.Aurelia aurita
has an interesting life history. The sexes are separate, the sperm are taken into the female via the mouth and fertilization occurs internally. Pits in the oral arms act as a temporary brood chamber holding the eggs until they develop into free-swimming larvae (planula larvae). Following a brief swimming period the planulae attach to hard substratum and develop into tiny sessile animals (scyphistomae). These reproduce by asexual budding and release free-swimming tiny immature jellyfish (ephyrae). The ephyrae feed on plankton and will generally reach maturity at around 3 months. However, some ephyrae may take up to two years to grow into sexually-reproducing adult medusae (Ruppert & Barnes, 1994).
Aurelia aurita feed, but not exclusively, on plankton and can at times occur in massive swarms, which may be so dense as to give the sea a uniform red colour and slow the passage of small boats (Russell, 1970).