As its name suggests, the common jellyfish (Aurelia aurita) is the most common jellyfish species on British shores (2). The body is a saucer shaped 'bell', which is colourless except for four obvious violet gonads visible in the centre of the disc (2). The outer edges are fringed with many small tentacles, and four stocky 'arms' surround the mouth (2).
The common jellyfish is carnivorous, and feeds mainly on a variety of planktonic species such as molluscs, crustaceans, young worms and copepods (3). The plankton is caught in a layer of mucus that covers the jellyfish. Tiny hair-like structures called 'cilia' on the body of the jellyfish produce currents by beating. These currents transport the captured plankton towards the edge of the 'bell', where it is removed with the arms and passed to the mouth (2). The tentacles around the margins of the bell and the arms bear stinging cells, which are occasionally used to catch small fishes and other prey (2).
In the common jellyfish, the sexes are separate and fertilisation occurs internally; the sperm is taken into the female's body via the mouth (2). The fertilised eggs undergo development in pockets in the arms that surround the mouth. The free-swimming larvae (known as 'planulae' larvae) are released during autumn; after some time these larvae settle and develop into tiny sessile animals ('scyphistomae'), which reproduce asexually and release free-swimming tiny immature jellyfish (called 'ephyrae'), which feed on plankton and become mature after around 3 months (2).
Of asexual reproduction: reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by fission (or in plants ‘vegetative reproduction’); part of the organism breaks away and develops into a separate individual. Some animals, including vertebrates can develop from unfertilised eggs, this process, known as parthenogenesis gives rise to offspring that are genetically identical to the parent.
When gametes (male and female reproductive cells) fuse to produce an embryo, which grows into a new individual.
Stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Aquatic organisms that drift with water movements; may be either phytoplankton (plants), or zooplankton (animals).
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