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Phylum Arthropoda > Subphylum Crustacea > Class Malacostraca > Order Decapoda > Braychurans
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For nature guides: introducing crabs
updated Apr 2020

What are crabs?
Have you ever eaten a crab? Almost everyone knows what a crab looks like! It has a hard shell, many legs, a pair of pincers. Next time, look closely at the crab you are eating.

Crabs belong to a group of animals called crustaceans. Other crustaceans include shrimps and prawns.

Shapes of crabs
The shapes of crabs tell us how they live.

  • Can you guess from the its legs how this crab lives?
  • Can you guess from its pincers what this crab eats?
    • Large crushing pincers: snails and clams
    • Spoon shaped tips: scraping algae
    • Sharp, toothed pincers: snagging fishes
    • Small delicate pincers: harvesting small bits

  • Why is this crab so colourful?
  • What is growing on this crab? Sometimes, swimming crabs have seaweed and barnacles growing on them. These crabs are usually infected by parasitic barnacles.

Marvellous moulting

  • Is this a crab dead or alive? No it's not alive. No it's not dead either! It's just an empty shell! Some fascinating moulting facts
    • Crabs and other hard-shelled animals moult to get bigger. When they moult they also regenerate lost limbs.
    • The soft-shelled crab that you eat is a crab that has just moulted.
    • When a crab has just moulted and the skin is still soft, it swallows water so that the skin hardens to be a little larger. That is why sometimes when you eat crabs they are watery.
    • Crabs can also only mate when the female has just moulted. So sometimes, males hold on to a female that is just about to moult so that he can be the first to mate with her.
    • More about moulting

  • How can you tell the difference between a dead crab and a moult?
    • A moult has transparent eyes and is light.
    • A dead crab is heavy and smells bad!

Crabs are important to the ecosystem

  • Like you, many animals love to eat crabs! They are an important part of the food chain in the ecosystem. Can we think of some animals that might eat a crab? Some charismatic animals to highlight: otters, shorebirds, other crabs, fishes.

Crab myths to dispel

  • Not all crabs can be eatenIn fact, some crabs can be highly poisonous. The poison is not destroyed even by cooking. Don't eat crabs that you caught yourself from the wild.

Handling tips

Finding crabs: Almost every shore will have some sort of crab. Small ones clamber on rocky shores, others are buried on sandy shores, while yet more scurry about among seagrasses, coral rubble and reefs.

Moults are interesting too! These are commonly seen on the high shore. You can even tell stories about them when the tide is too high, or while waiting out the wet weather in a shelter.

Be gentle! Do not poke or prod try to catch crabs. Try to observe crabs without capturing them. Use a moult to show parts of the crab.

Beware! Crabs can pinch! Large crabs can give a good pinch. Don't let small children handle them.
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