Jellyfish - Cnidaria

Gelatinous umbrella shaped bell with long tentacles flowing underneath around the mouth. The bell for moving, and the tentacles for catching prey. This what we know as the jellyfish. In reality, they should be called Jellies because their body is nothing of a fish.
They're found in every ocean, from the surface, to the sea floor, the most colourful lurk around coastal zones. Theses strange creatures have roamed the sea for at least 500 million years, being the oldest multi-organ animal alive.

A group of jellies is called a "Bloom", a "Smack" or "Swarm".
Jellies form in the same way as Anemones (almost like plants), but instead of staying clinging to the rocks, they have an extra phase of their development and are released into the open sea to swim around.

There are problems around the world in places where either global warming has killed the jellies' predators, or over fishing has had the same effect, causing the jellyfish populations to increase so greatly that it's dangerous to swim, and they're taking over the seas.
Smallest Jellie, Irukanji Jellyfish, is around one millimetre and the largest, Lion's mane jellyfish, is up to 2 metres in diameter.
Most have lethal stinger on their tentacles, but a few, like the moon jellyfish that's commonly found around New Zealand, won't sting if you were to pick it up.

They're strange little critters, but somehow extremely fascinating and gracious.