Crab
Crabs are decapod crustaceans, most of which belong to the infraorder Brachyura, often called true crabs.
Crabs are decapod crustaceans, most of which belong to the infraorder Brachyura, often called true crabs. They typically have a broad shell, a short abdomen folded under the body, and a first pair of legs modified into claws or pincers. Crabs live in marine, freshwater, and terrestrial habitats, and thousands of species are known.
Classification
Crabs are crustaceans in the order Decapoda, and true crabs are usually classified in the infraorder Brachyura. Some crab-like animals belong to other groups, including anomurans such as hermit crabs.
Anatomy and movement
Crabs generally have a broad carapace, stalked eyes, and a short abdomen folded under the body. Many move sideways, and the front pair of legs forms claws or pincers used for feeding and defense. They have a hard exoskeleton and five pairs of legs, with the first pair modified into pincers.
Habitat and diversity
Crabs live in marine, freshwater, and terrestrial environments, though most species are marine. Sources estimate roughly 7,000 to 10,000 described species, depending on the reference used.
Ecology and diet
Crabs fill many ecological roles, including scavenger, predator, and herbivore. Their diets and feeding habits vary widely across species. Many crabs are omnivores or scavengers.
Key facts
- Crabs are decapod crustaceans with five pairs of legs, including a front pair modified into pincers.
- Most authorities place true crabs in the infraorder Brachyura.
- Crabs occur in oceans, fresh water, and on land.
- Many crabs are omnivores or scavengers, though diets vary by species.
- Crab-like animals such as hermit crabs are not true crabs.
Crabs are familiar to Canadian readers through Atlantic and Pacific fisheries, seafood markets, and coastal ecosystems, especially along British Columbia and Atlantic Canada.
Frequently asked questions
What is a crab in biological terms?
How many legs do crabs have?
Do all crabs live in the ocean?
Are hermit crabs true crabs?
What do crabs eat?
References
- Encyclopaedia Britannica — https://www.britannica.com/animal/crabSupports: Definition of crab as a decapod crustacean; habitat range; approximate species count; mention of true crabs and related groups.
- Encyclopaedia Britannica — https://www.britannica.com/summary/crabSupports: Broad overview of crab anatomy, habitat, movement, diet, and examples.
- Wikipedia — https://en.wikipedia.org/wiki/BrachyuraSupports: Brachyura as the infraorder of true crabs; fossil record timing; approximate extant species count.
- Simple English Wikipedia — https://simple.wikipedia.org/wiki/CrabSupports: Basic anatomy, habitat diversity, and approximate number of known species.
- Oxford Learner's Dictionaries — https://www.oxfordlearnersdictionaries.com/us/definition/english/crabSupports: Basic description of crab body form, legs, pincers, and sideways movement.
- Britannica Kids — https://kids.britannica.com/kids/article/crab/353009Supports: Species count, habitats, hard exoskeleton, leg count, and feeding habits.