What are the external features of a crab?

1. Carapace: The dorsal (top) part of the crab's exoskeleton is called the carapace. It serves as a protective covering and encloses the crab's internal organs.

2. Rostrum: The rostrum is a forward-projecting beak-like structure on the front of the carapace. Its shape varies among different crab species.

3. Eyes: Crabs have a pair of stalked, compound eyes located on the front of the carapace. Each eye consists of numerous visual units called ommatidia, which allow the crab to see in multiple directions simultaneously.

4. Antennules and Antennae: Crabs possess a pair of antennules and a pair of antennae on the front of their heads. The antennules are smaller sensory organs located near the eyes, while the antennae are longer and serve for sensing their surroundings and detecting odors.

5. Mandibles and Maxillipeds: The mouthparts of a crab include a pair of mandibles, which are used for cutting and grinding food, and three pairs of maxillipeds, which are modified limbs assisting in feeding and food manipulation.

6. Chelipeds: The first pair of legs in most crabs is modified into chelipeds, which are strong and equipped with claws. Chelipeds are primarily used for capturing, cutting, and manipulating food, defense, and grasping objects.

7. Walking Legs: The remaining four pairs of legs are used for walking and are collectively called walking legs or pereiopods. The structure of the legs can vary, with some species having flattened legs for paddling or swimming.

8. Swimmerets: Male crabs have modified swimming legs, known as swimmerets or pleopods, used for transferring sperm during mating. Some female crabs also have swimmerets, which aid in holding and protecting their eggs attached to the underside of their abdomen.

9. Abdomen: The abdomen of a crab is typically tucked under the carapace and is narrower than the cephalothorax. It houses vital organs and appendages, including the reproductive organs.

These external features collectively contribute to the distinctive appearance and functionality of crabs, allowing them to adapt and survive in their respective habitats.