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