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 island 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, fishermen 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 a planet the Fourth Doctor and Romana II 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)