Animal structures

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Across
  1. 3. oxygen and carbon dioxide moves in and out of this internal structure
  2. 5. fish and reptiles have this type of rough external structure
  3. 7. a snail is protected by this hard external structure
  4. 8. birds have a lot of this external structure
  5. 10. the large group of animals that have bones as internal structures
  6. 12. mammals have this external structure to keep warm
  7. 14. humans have this external structure to protect all our internal structures
  8. 15. the part of the skeleton that protects the head
  9. 16. the part of the skeleton that straightens our back
Down
  1. 1. this sharp and pointy external structure can be used to attack other animals
  2. 2. insects use these external structures to fly
  3. 4. a dolphin is not a fish, but a _____________
  4. 6. a fish breathes using this internal structure
  5. 7. the rigid support system that contains bones in an organism
  6. 9. the organism internal structure that pumps blood
  7. 11. an animal external structure that is very hard
  8. 13. the part of the skeleton that protects the chest
  9. 16. the internal structure that processes a lot of information