Adaptations of UK crabs

I created the following slideshow on the adaptations of UK crabs for a piece of Biology homework at school. This project links in nicely with what I already wrote about Decapods and me.

I hope this displays properly. Please add a comment if not, specifying your screen dimensions and browser. I can then look into it.

There is a text version below just in case.


Text version

Adaptations of UK crabs

David Ford, 7A1

Adaptations in animals

The process which enables organisms to adjust to their environment in order to ensure survival.

The 3 types of adaptation

Structural: Physical features of an organism that enable them to survive in their environment (e.g. a penguin has blubber to protect itself from freezing temperatures)

Behavioural: Actions of an organism that enable them to survive in their environment (e.g. bears hibernate in winter to escape the cold temperatures and preserve energy)

Physiological: Internal and/or cellular features of an organism that enable them to survive in their environment (e.g. snakes produce poisonous venom to ward off predators and to capture prey)


True crabs and others

Brachyura are true crabs.
Anomura are crab-like species.
The crab shape is so successful that other decapod species have adapted to it, though there are always subtle differences.

Examples of crab adaptations


  • Claws
  • Carapace
  • Colour
  • Size


  • Nocturnal
  • Camouflage
  • Concealment
  • Migration


  • Moulting
  • Life cycle
  • Regeneration

Adaptations across groups of crabs

Some crabs species can be grouped by common adaptations.

Here we look at the following groups:

  • Swimming crabs
  • Hermit crabs
  • Spider crabs

Adaptations of swimming crabs

The rear-most legs of this group are flattened like paddles, helping them swim more effectively.

Adaptations of hermit crabs

Hermit crabs have one small feeding claw and one large defence claw. When retreating into their shell the defence claw seals the opening protecting the hermit crab inside.

Hermit crabs also have a strong sense of smell. They can detect food from a considerable distance. They like to try new foods but can also remember the smell of a previous meal.

Adaptations of spider crabs

The carapace of a spider crab is covered in protrusions which helps break up its outline and allow it to blend in against rocks and weed.

They can use their claws to tear bits of seaweed or sponge away from rocks. They then decorate themselves with it for better camouflage.

Adaptions of specific species

Ultimately, different species are set apart by their own adaptations.

Here we look at just a few representative cases:

  • Shore crabs (Carcinus maenas)
  • Masked crabs (Corystes cassivelaunus)
  • Pea crabs (Pinnotheres pisum)

Adaptations of Shore crabs (Carcinus maenas)

Osmoregulation: The process by which cells and simple organisms maintain fluid and electrolyte balance with their surroundings.

As the only UK crab with this adaptation, Shore crabs are able to thrive in estuaries where the water is brackish (less salty) and other crabs cannot survive.


Adaptations of Masked crabs (Corystes cassivelaunus)

Masked crabs are nocturnal. During the day they bury themselves in sand in order to hide from predators.

These crabs have an antenna which is adapted as a sort of snorkel, allowing sea-water to circulate to its gills when buried in sand.

Adaptatons of Pea crabs (Pinnotheres pisum)

Pea crabs live in the mantle cavity of certain bivalve molluscs. For this they need to be small. UK pea crabs are approximately 10mm.

The pea crab relies solely on its commensalist host for food, safety, and oxygen.

Challenges for the future

Adapting to:

  • Artificial environments: learning to live in or with man-made structures
  • Climate change: coping with changes to weather patterns and seasonal variations
  • Invasive species: resisting the onslaught as new species keep arriving as unintended passengers on ships and boats

David’s Rockpool Discoveries

If you like this presentation please visit my website:

  • My discoveries on family trips to the coast
  • Some research into things that interest me
  • Book reviews
  • Quizzes


Definitions of Adaptations and the 3 types:

Information about Shore crabs, especially that about Osmoregulation


Leave a Reply

Your email address will not be published. Required fields are marked *