information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Moon jellyfish (Aurelia aurita)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.



Aurelia aurita 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.

Recorded distribution in Britain and Ireland

Aurelia aurita can be found all round the coasts of Britain and Ireland.

Global distribution



Aurelia aurita is Britain's most common jellyfish. It is sporadic in its appearance, forming massive local populations in some areas but totally absent in other areas for some years. Aurelia aurita is a pelagic species but may be found washed up on the shore. It is known to occur up estuaries and into harbours and is especially common in Scottish sea lochs.

Depth range


Identifying features

  • Umbrella thins towards the edge and has a distinctive fringe of short, hollow tentacles.
  • Four, purple-blue gonads form a characteristic horseshoe-shape, contained almost completely within the gastric cavity.
  • Gonads do not extend below the sub-umbrella surface as in many other species of jellyfish.

Additional information

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).

Listed by

- none -

Further information sources

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  1. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  2. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

  3. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

  4. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.

  5. Ruppert, E.E. & Barnes, R.D., 1994. Invertebrate zoology (6th ed.). Fort Worth, USA: Saunders College Publishing.

  6. Russell, F.S., 1970. The medusae of the British Isles. Vol II - Pelagic Scyphozoa, with a supplement to the first volume on hydromedusae. Cambridge University Press


This review can be cited as:

Heard, J.R. 2004. Aurelia aurita Moon jellyfish. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 23-09-2018]. Available from:

Last Updated: 07/10/2004