Image Key > Cnidaria > Scyphozoa

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Aurelia sp.

Taxonomy

• Range in diameter from 20 mm to 1 m or more.

• Most have bell-shaped bodies.
• Tentacles (when present) are found around the edge of the bell, which is usually scalloped.
• Other prominent features include conspicuous oral arms, which can be mistaken for tentacles, present under the centre of the bell.
• One opening, a mouth that lies at the base of the oral arms, leads straight into the gut.

• Approximately 250 species are known worldwide, with about 10 common along the temperate Australian coast.

• The gonads are often crescent-shaped organs that develop in four compartments in the stomach floor.
• The medusa is the adult, free-swimming jellyfish. It has the familiar umbrella-shaped bell, tentacles and oral arms, and reproduces sexually.
• In most species, male and female medusae spawn into the sea where the eggs are fertilized.
• The fertilized egg, a pear-shaped organism that moves with the aid of cilia (tiny hairs), is called a planula.
• The planula eventually swims to a hard surface, attaches itself, and slowly transforms into a polyp, which can be inconspicuous (or even absent in some species).
• The polyp is called a scyphistoma and has a tubular body with a mouth and ring of tentacles on the top.
• During favourable conditions the scyphistoma divides transversely into a stack of medusae, which then separate and swim away.