How to Identify and Classify Crabs - Exam
  • 1. Which feature is MOST important for initial crab classification?
A) Body shape
B) Eye color
C) Claw size
D) Leg length
  • 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 live only in freshwater
C) False crabs are larger
D) True crabs have more legs
  • 3. Which crab shape is characteristic of Brachyura (true crabs)?
A) Round and bulbous
B) Long and narrow
C) Star-shaped
D) Broad and flattened
  • 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) Chelipeds
B) Pleopods
C) Uropods
D) Pereiopods
  • 6. How many pairs of walking legs do most true crabs have?
A) Three
B) Six
C) Four
D) Five
  • 7. The small abdominal flap on the underside of a crab is used for what?
A) Swimming
B) Camouflage
C) Digging
D) Reproduction
  • 8. How can you typically determine the sex of a crab?
A) By the length of the legs
B) By the shape of the abdominal flap
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) Female crab
C) Hermaphrodite crab
D) Juvenile crab
  • 10. A narrow, V-shaped abdominal flap generally indicates a:
A) Male crab
B) Hybrid crab
C) Female crab
D) Immature crab
  • 11. What is the function of gills in crabs?
A) Waste removal
B) Sensory perception
C) Food digestion
D) Oxygen extraction
  • 12. Where are crab gills typically located?
A) On the abdomen
B) Within the gill chambers beneath the carapace
C) Externally, attached to the body
D) On the legs
  • 13. What is the function of the crab's carapace?
A) Respiration
B) Digestion
C) Protection
D) Locomotion
  • 14. Which of these is a key feature to identify spider crabs?
A) Large, symmetrical claws
B) Long legs relative to their body size
C) Brightly colored carapace
D) Paddle-like swimming legs
  • 15. Which crabs are known for their ability to run sideways quickly?
A) Hermit crabs
B) King crabs
C) Stone crabs
D) Ghost crabs
  • 16. What type of crab is known for carrying a shell for protection?
A) Hermit crab
B) Snow crab
C) Box 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) Decorator crab
B) Coconut crab
C) Mud crab
D) Pea crab
  • 19. What is the scientific term for molting in crabs?
A) Metamorphosis
B) Regeneration
C) Ecdysis
D) Osmoregulation
  • 20. Why do crabs molt?
A) To reproduce
B) To change color
C) To grow larger
D) To shed parasites
  • 21. What is the 'crab' in 'horseshoe crab'?
A) A misnomer, they are more closely related to spiders and scorpions.
B) An accurate descriptor, it's a type of crab.
C) They were once classified as crabs but have since been reclassified.
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) 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) Marginal setae
B) Epipods
C) Rostral spines
D) Branchial ridges
  • 24. What is the primary diet of most crabs?
A) Omnivorous
B) Herbivorous
C) Carnivorous
D) Detritivorous
  • 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) Specialized lungs
D) Waterproof carapace
  • 26. What is the function of the uropods in some crab species?
A) Sensing vibrations
B) Defense
C) Feeding
D) Swimming
  • 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) Cyprid
B) Megalopa
C) Zoea
D) Nauplius
  • 29. Which crab is known for its bright red color and is often harvested for food?
A) Red king crab
B) Blue crab
C) Snow crab
D) Dungeness crab
  • 30. How do crabs communicate?
A) They don't communicate
B) Primarily through vocalizations
C) Only through tactile signals
D) Through visual and chemical signals
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