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