Crab

Crabs were a type of crustacean found on several planets, including Earth. These crabs sometimes grew or evolved into giant crabs, such as those that lived on the islands of the planet Salutua. (PROSE: The Eye of the Giant)

On Earth crabs were utilised as a food source, basing themselves along the coastline such as the Cornish coast, fisherman such as Charlie Johns fished for them. (PROSE: Rip Tide)

On one planet crabs were, as the Sixth Doctor and Peri Brown discovered genetically-engineered to become more intelligent. (PROSE: Shell Shock)

Giant hermit crabs existed on an unnamed planet the Fourth Doctor and Romana once visited. (PROSE: The Little Things)

On at least two different planets the Doctor encountered violent crabs; in his first incarnation whilst travelling with John and Gillian they encountered a large crab in a sea on a desolate planet. These crabs appeared vicious and one attacked John, but the Doctor was able to drive it off with his electroliser. (COMIC: Shark Bait) While on the planet Praxos 9 the Tenth Doctor and Rose Tyler also encountered violent crabs and had to fight off luminous sucker crabs whilst on the planet. (COMIC: Blood and Tears)

Whilst in the Divergent Universe the Eighth Doctor, Charley Pollard and C'rizz encountered giant crabs on an island during their travels through the universe without time. (AUDIO: The Next Life)

Crab-like species
The Macra appeared to have evolved from crabs or crab-like creatures. (TV: The Macra Terror)