Invertebrate Zoology - Molluscs - snails, clams, sea-slugs and relatives

What Animals are Included in the Overview?

What are invertebrates?
The term "invertebrates" is used to refer to all animals without a backbone. It is not a natural grouping, unlike the vertebrates (mammals, birds, reptiles, amphibians and fish) which are related through their evolution. The invertebrates include over thirty phyla with very different features and evolutionary histories.

The marine invertebrates include animals as diverse as molluscs (shelled animals like snails and clams, as well as sea slugs, squid & cuttlefish), crustaceans (e.g. crabs, barnacles, shrimp), many different types of worms (e.g. bristle worms, flatworms, acorn worms, spoon worms), jellyfish and sea anemones, and echinoderms (sea stars, sea cucumbers, sea urchins etc). They also include several groups which some people may not even realise are animals, such as corals (related to sea anemones) and sponges.

How many species are there?
No-one can say exactly how many species are involved, since many groups, particularly those which are very small or obscure, have not been well studied. Even the better known groups still have many undescribed species. Tens of thousands of Australian marine invertebrates have already been described, with many more still awaiting discovery.

What habitats do they occupy?
Marine invertebrates are found in all marine habitats ranging from shorelines and estuaries down to the barely explored habitats of the abyssal sea (which reaches depths of up to 11,000 metres in some of the deepest ocean trenches). In addition to well-known habitats such as rocky shores and rockpools, coral reefs and seagrass beds, marine invertebrates can be found in the spaces between grains of sand, around hydrothermal vents, on floating debris such as algal mats and driftwood, attached to other animals, and on the peaks and slopes of seamounts ("underwater volcanoes"), as well as swimming or floating in the water itself.

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