Crab Definition | Characteristics & Facts


Crab Definition

A crab is a crustacean belonging to the infraorder Brachyura. Crabs are characterized by their flat bodies, strong exoskeleton, and ten legs, including a pair of pincers (chelipeds). They are predominantly marine creatures, although some species also inhabit freshwater and terrestrial habitats.

Crab General Characteristics & Facts

  • Crabs are crustaceans, belonging to the order Decapoda, which means “ten feet” referring to their five pairs of legs.
  • They are found in various aquatic environments worldwide, including oceans, freshwater lakes, and rivers. They are also well adapted to living in intertidal zones, where they scuttle along the shorelines.
  • Crabs have a distinctive sideways or “crab-like” walk, moving by scuttling sideways with their legs. This unique locomotion is due to the structure of their legs and the placement of their joints.
  • They come in various shapes, sizes, and colors, with over 7,000 known species of crabs. Some common types include blue crabs, fiddler crabs, hermit crabs, and king crabs.
  • Crabs have a specialized respiratory system with gills that allow them to extract oxygen from water. Some species can also breathe air when out of the water for extended periods.
  • They are primarily scavengers or opportunistic omnivores, feeding on a wide range of food including algae, small fish, mollusks, detritus, and even carrion.
  • Many crab species have remarkable adaptations, such as camouflage to blend with their surroundings, strong claws for defense and capturing prey, and regenerative abilities to regrow lost limbs.
  • Reproduction in crabs involves a complex courtship ritual, with males often engaging in displays to attract females. Females lay eggs, which they carry with them until they hatch into larvae and are released into the water.
  • Crabs are a popular food source for humans and are harvested for culinary purposes in many cultures. Sustainable fishing practices are crucial to ensure the conservation of crab populations.
  • Crabs play important ecological roles, such as helping to control populations of other organisms, recycling nutrients, and serving as prey for larger predators. They contribute to the overall health and balance of aquatic ecosystems.

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Physical Characteristics of Crab

  1. Exoskeleton: Crabs have a hard, calcified exoskeleton that covers and protects their body. The exoskeleton is made up of a series of plates or segments that are joined together, providing support and defense against predators.
  2. Carapace: The carapace is the hard, convex shell that covers the crab’s cephalothorax (the fused head and thorax region). It acts as a protective shield for the internal organs.
  3. Legs: Crabs have ten legs, with each leg serving a specific purpose. The first pair of legs, known as chelipeds, are modified into large pincers (chelae) used for defense, feeding, and handling objects. The other eight legs are used for walking, swimming, and maneuvering.
  4. Claws: The pincers or claws of crabs come in various shapes and sizes, depending on the species and their specific needs. The claws can be used for defense, capturing prey, and manipulating food.
  5. Eyes: Crabs have compound eyes, which are made up of many individual light-sensing units. These eyes provide excellent peripheral vision and enable crabs to detect movement and potential threats.
  6. Gills: Crabs have specialized gills located in the branchial chambers beneath the carapace. The gills extract oxygen from water, allowing crabs to respire and obtain oxygen for survival.
  7. Abdomen: The abdomen of a crab is located on the underside of the body. It is soft and flexible, allowing for movement and accommodation of internal organs. In male crabs, the abdomen is narrower, while in female crabs, it is broader to accommodate the eggs during reproduction.
  8. Coloration and Camouflage: Crabs exhibit a wide range of colors and patterns, often providing effective camouflage against their surroundings. This coloration helps them blend into their environment and avoid predators.

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Scientific Classification of Crab

Kingdom: Animalia (Animals)

Phylum: Arthropoda (Arthropods)

Subphylum: Crustacea (Crustaceans)

Class: Malacostraca (Malacostracans)

Order: Decapoda (Decapods)

Infraorder: Brachyura (Crabs)

Key Locations of crab without description?

  • Coastal Areas
  • Intertidal Zones
  • Coral Reefs
  • Estuaries and Mangroves
  • Salt Marshes
  • Freshwater Environments
  • Deep-Sea Environments

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Crab FAQs

What does a crab eat?

  1. Small Fish
  2. Invertebrates
  3. Plant Matter
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