Sydney Hydroid Corals

Hydroids are very tiny and insignificant.However, they occur in prolific numbers. They are far more primitive and simple than other corals. In the sea, they live in prodigious numbers and inhabit many zones in the sea. There are clumps living on Kelp, on rocks, in caves and everywhere.There are several major types of Hydroids. Feathery Hydroids, Solitary Hydroids, Colonial and Drifting species.

The Feathery Hydroids are Stinging Hydroids. These tiny polyps are extremely delicate and live inside a see through glass cup. Each little feather can have thousands of cloned polyps. A small clump of Feathery Hydroids can have half a million polyps in less than a square metre.

Other related groups include Fire Corals, Pink Stylaster coral , Solanderiae Fan corals and Bluebottles. Fire corals live in cement houses. Solanderia live on a fan like structure.

Blue bottles, Physalia are a colony of polyps which have become specialised. One polyp has become a float, some polyps trap and kill food, some polyps produce reproductive cells. The Vellela or By the Wind Sailor are also a Hydrozoan.


Hydroids Hydroid feathery
Feathery Hydroids have very beautiful little polyps when seen under a microscope. Each tiny polyp lives in a glass "cup". They can give a quite powerful sting. A Feathery Hydroid is fighting for living space with this sponge. Numbers of Hydroids can be mindblowing. Each branch of these feathers can have scores of hydroids on each side. There would easily be tens of thousands of tiny polyps just in this tiny clump. Large clumps can contain hundreds of millions of perfectly formed little killing machines. They are all clones of each other.
This Fijian Aeolid sea slug feeds on Hydroids. It eats immature hydroids and stores them in the tips of its serrata. When they mature, these stinging cells confer the ability to sting onto the Sea Slug. The yellow coloured tips on the ends of each serrata contain the nematocysts in a 'bag' called a Cnidosac'.. The Solitary Hydroid is a giant in tne world of Hydroids. It has no supporting structure around its polyp.