Story: Corals, anemones and jellyfish
Corals, sea anemones and jellyfish all belong to the same large group of animals – cnidarians. The name comes from the Greek ‘knide’, meaning nettle – they carry a sharp sting in their tentacles. One of the most notorious is the Portuguese man-of-war, which is not a single creature; this pirate of the high seas is actually a colony of highly specialised individuals.
Full story by Dennis Gordon
Main image: Jewel anemone
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When we clamber around New Zealand’s rocky shores, or walk along its beaches, we might poke our finger into the waving tentacles of a sea anemone or, if we are unlucky, we might be stung by a washed-up jellyfish.
What do corals, anemones and jellyfish have in common?
Sea anemones and jellyfish look very different, yet they are both related. Corals are also a close cousin. They all belong to a group called cnidarians (pronounced ‘nid-air-e-ans’), also known as the ‘nettle animals’, because they have stinging tentacles.
Cnidarians have a simple body, with a single opening surrounded by a ring of tentacles. They can have two forms:
- the medusa or jellyfish phase, where they are free swimming
- the polyp phase, where they attach themselves to a surface.
Corals and anemones
We often think of corals growing only in tropical reefs, but New Zealand has 127 species in its waters. Corals are not always what they seem. They look like hard branching plants, but this is actually the framework of thousands of soft polyps which live around it. They reach their tentacles out from this framework to search for food.
There are two types of corals:
- Hexacorals can be single animals, or live in groups, sharing body tissues. Most hexacorals are anemones, which you will find in rocky pools.
- Octocorals have eight tentacles. New Zealand has 243 species of octocoral.
There are three main types of jellyfish:
- Swimming jellyfish live in sea water, and you can sometimes find them washed up on the beach.
- Stalked jellyfish cannot swim (they float and somersault), and are rare in New Zealand waters.
- Box jellies are square-shaped and among the most deadly creatures in the world.
One infamous ‘jellyfish’, the Portuguese man-of-war, is not a jellyfish at all. It is a siphonophore, which is a colony of tiny creatures living together and performing special tasks. Some make up the stomach, some are responsible for movement, and others carry out reproduction.