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How to Identify and Classify Crabs - Exam
Contributed by: Wallis
  • 1. Which feature is MOST important for initial crab classification?
A) Body shape
B) Claw size
C) Eye color
D) Leg length
  • 2. What is the difference between true crabs and false crabs?
A) False crabs are larger
B) True crabs have more legs
C) False crabs live only in freshwater
D) True crabs have a reduced abdomen tucked under the cephalothorax
  • 3. Which crab shape is characteristic of Brachyura (true crabs)?
A) Round and bulbous
B) Broad and flattened
C) Long and narrow
D) Star-shaped
  • 4. What term describes the fused head and thorax of a crab?
A) Prosoma
B) Carapace
C) Abdomen
D) Cephalothorax
  • 5. Which appendage is typically modified into large claws in crabs?
A) Pereiopods
B) Uropods
C) Chelipeds
D) Pleopods
  • 6. How many pairs of walking legs do most true crabs have?
A) Four
B) Three
C) Six
D) Five
  • 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 length of the legs
C) By the color of the carapace
D) By the size of the claws
  • 9. A wide, U-shaped abdominal flap generally indicates a:
A) Male crab
B) Juvenile crab
C) Hermaphrodite crab
D) Female crab
  • 10. A narrow, V-shaped abdominal flap generally indicates a:
A) Hybrid crab
B) Female crab
C) Male crab
D) Immature crab
  • 11. What is the function of gills in crabs?
A) Oxygen extraction
B) Waste removal
C) Sensory perception
D) Food digestion
  • 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) Digestion
C) Respiration
D) Locomotion
  • 14. Which of these is a key feature to identify spider crabs?
A) Large, symmetrical claws
B) Paddle-like swimming legs
C) Brightly colored carapace
D) Long legs relative to their body size
  • 15. Which crabs are known for their ability to run sideways quickly?
A) Stone crabs
B) Ghost crabs
C) King crabs
D) Hermit 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) One greatly enlarged claw in males
C) A flattened, shovel-like carapace
D) The ability to climb trees
  • 18. Which crab is commonly found in saltwater marshes and mudflats?
A) Mud crab
B) Decorator crab
C) Coconut crab
D) Pea crab
  • 19. What is the scientific term for molting in crabs?
A) Ecdysis
B) Osmoregulation
C) Regeneration
D) Metamorphosis
  • 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) A regional term for a certain type of true crab
B) A misnomer, they are more closely related to spiders and scorpions.
C) An accurate descriptor, it's a type of crab.
D) They were once classified as crabs but have since been reclassified.
  • 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) Branchial ridges
B) Marginal setae
C) Rostral spines
D) Epipods
  • 24. What is the primary diet of most crabs?
A) Carnivorous
B) Detritivorous
C) Omnivorous
D) Herbivorous
  • 25. Which adaptation allows some crabs to survive out of water for extended periods?
A) Modified gill chambers
B) Ability to absorb oxygen through their skin
C) Waterproof carapace
D) Specialized lungs
  • 26. What is the function of the uropods in some crab species?
A) Feeding
B) Swimming
C) Defense
D) Sensing vibrations
  • 27. Which group are considered 'false crabs' because of their flattened shape, despite not being true crabs?
A) King crabs
B) Shore crabs
C) Hermit crabs
D) Spider crabs
  • 28. What is the name of the larval stage of a crab?
A) Megalopa
B) Nauplius
C) Cyprid
D) Zoea
  • 29. Which crab is known for its bright red color and is often harvested for food?
A) Blue crab
B) Snow 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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