Jellyfish
Jellyfish are also cnidarians, like corals, but the jellyfish we are familiar with are usually the free-swimming medusa stage of their life-cycle.
Commonly stranded after a storm is the balloon-like bluebottle (Physalia) which is related to the Portuguese Man-o-War. This is actually a colony, each polyp specialising in a function such as an air bladder or a stinging tentacle. Two disc-shaped jellyfish with hanging tentacles are occasionally found – Velella with its little sail and Porpita without a sail.
Physalia tentacles can sting quite severely, even when dried, but the other two are harmless.
Common name
Bluebottle
Scientific name
Physalia physalis
Description
This aptly-named jellyfish is often beached in large numbers after a storm. Surprisingly, a bluebottle is not an individual, but a colony of specialised polyps. Some capture food, some digest the food, some reproduce and one becomes the gas-filled float. The sting is very painful. The local bluebottle is closely related to the Portuguese Man-o-war which occurs in northern Australian waters and overseas.