Molluscs

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Molluscs are invertebrates, which means they are creatures that have a soft body and no skeleton inside of them.

There are many different species of mollusc in the sea, including squid, sea snails, oysters, mussels and octopuses. All these species are very different to each other, they look different and they protect their bodies using different types of shells.

You would find most types of molluscs living in the deep parts of the sea or along the sea floor. There are some molluscs which live on land such as snails and worms.

Sea Snail

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Mussels

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Octopuses

Octopuses are a type of a mollasc that do not have any kind of shell. They have eight tentacles type arms, although two of these tentacles act more like legs and they use them to push themselves off when swimming or to ‘walk’ across the ocean floor, helping them to move along through the water. If they loose a tentacle they can regrow it so they will always have eight whatever happens.

Octopuses are incredibly clever creatures and have been seen doing all sorts of amazing things such as using objects as tools. They often like to use shells they find on the sea floor to hide in or carry objects as protection from predators. They can learn how to do new things just by watching other octopuses doing something.

Octopuses do get attacked by other creatures but have very good ways of hiding or getting away from them. They can camouflage themselves so they can hide from predators, disappearing into their background. They can also confuse predators by squirting out ink which gives them a chance to escape!

There are over 300 species of octopuses living in the oceans of the world. They can be found all over the world in many different habitats. Many species of octopuses like to live in protected environments such as coral reefs or will build their own shelter out of shells and other objects.

Blue Ringed Octopus

This is the most dangerous octopus to humans because their venom is powerful enough to kill us. It is not a scary creature to look at though as it is tiny, growing no bigger than a ruler. Most of the time it is brown/grey colour but when it gets angry or scared lots of bright blue rings appear probably as a warning and a way of scaring off predators.

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Giant Pacific Octopus

This is the largest Octopus swimming around in the ocean, growing up to about 5 metres long although even bigger ones have been found. They often live longer than most Octopuses, living for about 4 years.

Giant Pacific Octopus by vidalia_11 CC BY 2.0

Did you know...

Octopuses are dangerous predators and like to eat other sea creatures. They often catch their prey by biting and injecting a venom into them to paralyse them so they can't move before eating them!

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Squid

A Squid’s body is made up of a mantle (its body), eight arms and two longer tentacles. They have an internal shell called a cuttlebone.

It has suckers on its arms and tentacles which have sharp spikey edges. These help the squid catch their prey and make it difficult for them to get away! Where their arms and tentacles meets its body it has a beak, which it uses to eat its prey.

A squid moves through the water by pulling water into the empty space in its mantle and then pushing it back out. This shoots them forward as they push the water out. They breathe through gills in their mantle.

In between their gills they have an ink sack which they shoot ink out of if under attack. When they squirt ink out into the water it makes it harder for its attacker to see and lets them make a quick escape.

Two of the most interesting squid are very difficult to photograph as they are so big and live in the dark depths of the oceans. These are Giant Squid and Colossal Squid.

A Giant Squid is very big, they can grow to be up to 13 metres long. They have huge eyes, which measure just a bit smaller than a 30cm ruler. It is found in many oceans around the world but likes to live all the way down in the deepest part of the water. This makes it difficult to learn more about them because they live in such cold and dark places it is really hard for divers to find them. It is thought that the Giant Squid lives all over the world, but not in really hot or cold water.

Colossal Squid are even bigger than Giant Squid! While growing to around 14 metres long they are heavier and more ‘solid’ than a giant squid. They have a bigger mantle, but probably have shorter tentacles. Their eyes are slightly larger than the Giant Squid but not bigger than a 30cm ruler. They have sharp hooks on the end of their tentacles, making it even harder for their prey to escape when caught. Colossal Squids are found in the cold waters around Antarctica.

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