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