How to Identify and Classify Crabs
  • 1. Which feature is MOST important for initial crab classification?
A) Eye color
B) Claw size
C) Leg length
D) Body shape
  • 2. What is the difference between true crabs and false crabs?
A) True crabs have a reduced abdomen tucked under the cephalothorax
B) False crabs are larger
C) True crabs have more legs
D) False crabs live only in freshwater
  • 3. Which crab shape is characteristic of Brachyura (true crabs)?
A) Star-shaped
B) Long and narrow
C) Round and bulbous
D) Broad and flattened
  • 4. What term describes the fused head and thorax of a crab?
A) Prosoma
B) Carapace
C) Cephalothorax
D) Abdomen
  • 5. Which appendage is typically modified into large claws in crabs?
A) Pleopods
B) Uropods
C) Pereiopods
D) Chelipeds
  • 6. How many pairs of walking legs do most true crabs have?
A) Six
B) Three
C) Four
D) Five
  • 7. The small abdominal flap on the underside of a crab is used for what?
A) Swimming
B) Digging
C) Reproduction
D) Camouflage
  • 8. How can you typically determine the sex of a crab?
A) By the shape of the abdominal flap
B) By the color of the carapace
C) By the size of the claws
D) By the length of the legs
  • 9. A wide, U-shaped abdominal flap generally indicates a:
A) Male crab
B) Hermaphrodite crab
C) Juvenile crab
D) Female crab
  • 10. A narrow, V-shaped abdominal flap generally indicates a:
A) Male crab
B) Female crab
C) Hybrid crab
D) Immature crab
  • 11. What is the function of gills in crabs?
A) Food digestion
B) Waste removal
C) Sensory perception
D) Oxygen extraction
  • 12. Where are crab gills typically located?
A) Within the gill chambers beneath the carapace
B) On the legs
C) On the abdomen
D) Externally, attached to the body
  • 13. What is the function of the crab's carapace?
A) Protection
B) Respiration
C) Locomotion
D) Digestion
  • 14. Which of these is a key feature to identify spider crabs?
A) Paddle-like swimming legs
B) Brightly colored carapace
C) Long legs relative to their body size
D) Large, symmetrical claws
  • 15. Which crabs are known for their ability to run sideways quickly?
A) King crabs
B) Ghost crabs
C) Hermit crabs
D) Stone crabs
  • 16. What type of crab is known for carrying a shell for protection?
A) Hermit crab
B) Fiddler crab
C) Snow crab
D) Box crab
  • 17. What distinguishes fiddler crabs?
A) The ability to climb trees
B) One greatly enlarged claw in males
C) Brightly colored walking legs
D) A flattened, shovel-like carapace
  • 18. Which crab is commonly found in saltwater marshes and mudflats?
A) Pea crab
B) Coconut crab
C) Decorator crab
D) Mud crab
  • 19. What is the scientific term for molting in crabs?
A) Osmoregulation
B) Ecdysis
C) Regeneration
D) Metamorphosis
  • 20. Why do crabs molt?
A) To reproduce
B) To grow larger
C) To shed parasites
D) To change color
  • 21. What is the 'crab' in 'horseshoe crab'?
A) A regional term for a certain type of true crab
B) An accurate descriptor, it's a type of crab.
C) They were once classified as crabs but have since been reclassified.
D) A misnomer, they are more closely related to spiders and scorpions.
  • 22. Which of these is NOT a feature typically used for crab identification?
A) Internal organ structure
B) Claw shape
C) Carapace ornamentation
D) Leg structure
  • 23. The teeth-like projections along the front edge of a crab's carapace are called:
A) Branchial ridges
B) Epipods
C) Marginal setae
D) Rostral spines
  • 24. What is the primary diet of most crabs?
A) Carnivorous
B) Herbivorous
C) Detritivorous
D) Omnivorous
  • 25. Which adaptation allows some crabs to survive out of water for extended periods?
A) Ability to absorb oxygen through their skin
B) Specialized lungs
C) Modified gill chambers
D) Waterproof carapace
  • 26. What is the function of the uropods in some crab species?
A) Feeding
B) Defense
C) Swimming
D) Sensing vibrations
  • 27. Which group are considered 'false crabs' because of their flattened shape, despite not being true crabs?
A) Hermit crabs
B) Spider crabs
C) King crabs
D) Shore crabs
  • 28. What is the name of the larval stage of a crab?
A) Cyprid
B) Zoea
C) Megalopa
D) Nauplius
  • 29. Which crab is known for its bright red color and is often harvested for food?
A) Snow crab
B) Blue crab
C) Red king crab
D) Dungeness crab
  • 30. How do crabs communicate?
A) Primarily through vocalizations
B) Only through tactile signals
C) Through visual and chemical signals
D) They don't communicate
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