CRUSTACEAN ANATOMY

With about 15,000 species of decapods - there is a lot of variation. But all decapods have 10 legs, antennae, and an exoskeleton.

ANTENNAE

Decapods have eyes on stalks, which allows them to see all around them. What’s more, they have compound eyes. This means each eye contains thousands of small eyes within it - which are called ommatidia. Compound eyes are extremely good at detecting movement.

Dark crab with orange eyes and red claws

DID YOU KNOW?

Some decapods have scary looking eyes

- like the Golden Eye Vampire Crab.

Don't worry though, they are very small!

CLAWS

The claws on a decapod are the toughest part of the body. That’s because they are often used to catch prey and fend off predators. Also, they use their claws to dig and communicate with each other. Their claws come in two parts - a fixed “finger” and a moveable “finger”. Large claws are used for crushing, smaller claws can be used for slicing. Some have ridges between their claws to help them grip.

Fiddler crab with large claw on muddy ground

Small crustacean with yellow spots on an orange sponge

CRAZY CRUSTACEAN FACT!

Although smaller than a finger, The Pistol Shrimp is one of the deadliest animals on earth. How does it kill its prey? With bubbles!

It has a claw that snaps so fast it creates a ‘bubble bullet’ which is louder than a gun and hotter than lava. In short, it’s the most powerful cowboy in the sea.

CRUSTACEAN CHECK

Can you work out which "finger" is fixed, and which is moveable?

SIZE AND SHAPE

Decapods come in all shapes and sizes. Crabs have flat bodies, which allow them to squeeze into small spaces. Lobsters have longer bodies and a fan-shaped tail. Shrimps and prawns also have a tail, and tend to be a lot smaller.

Japanese spider crab showing impressive leg span

Blue and yellow sea slug on rocky seafloor.

Japanese Spider Crab has a leg span of up to 4m!

Female pea crabs grow up to 12 mm. Male pea crabs up to 8mm

Of course, every decapod starts off small - just like humans. In fact, they start off as a teeny tiny egg before going through several stages of transformation. To give an example, here is the life cycle of a crab:

Crab life cycle diagram: eggs, zoea, juvenile, adult crab

Unlike us, decapods do not have skin that stretches as they grow. When their shell gets too small they shed it and grow a new one. This process is called moulting.