Incredible drifters
Common jellyfish Bluebottle By-the-wind sailor Salp
Jellyfish are only one part of a two part story. Termed Hydrozoa, from the Greek 'sea animal', they exhibit 'alternation of the generations'. In one generation they are asexual, bottom dwelling polyps, and in the next they are sexual, free-swimming, gelatinous organisms known as the medusa, the floating jellyfish. They are colonies of specialised polyps, each with their own task such as reproduction, feeding, stinging, or movement.
(Aurelia aurita)
Habitat: Floating phase of its generation.
Identification: The common jellyfish is almost transparent apart from the deeper coloured, lobed reproductive organs. The animal consists of a hollow bell and deep saucer.
General: The jellyfish transparency stems from their body having an organic content of around 1%, the remainder being water. It moves by contracting muscles around the rim of the bell, which is also where its stinging polyps are located.
Other Names: Portuguese man-of-war. (Physalia physalis)
Habitat: Floating phase of its generation.
Identification: Has a gas filled float to keep the animal on the surface, and no bell shape to give movement of its own accord.
General: It has long tentacles which can be drawn up or let down at will. The tentacles have stinging polyps which act independently. If a small fish is stung it will be killed and drawn up into the stomach where it will be consumed. These jellyfish are commonly washed onto shore during summer months, the tentacles continuing to sting anything they touch, including swimmers.
(Velella velella)
Habitat: Floating phase of its generation.
Identification: The float is a flattened oval shape with a twisted sail mounted on top.
General: Large schools often form along the coast in summer.
Other Names: Chain Tunicate. (Doliolum)
Habitat: Floats freely in the sea.
Identification: A transparent, flexible tube shape varying from 1 cm across, to large enough for a diver to swim inside.
General: A member of the Tunicate, or sea squirt family. They are hermaphrodite invertebrates which form colonies.