Chordates and fishes

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Across
  1. 2. covers or closes aperture
  2. 3. small & transparent
  3. 6. teeth-like scales
  4. 9. release of excretory
  5. 13. top chamber of heart
  6. 14. sensory organs
  7. 15. fin on back
  8. 16. skeletal rod
  9. 17. bottom chamber of heart
  10. 18. deep-bodied
  11. 19. bottom-dwelling
  12. 20. fish having fleshy lobed fins
Down
  1. 1. helps control direction
  2. 4. two short siphons
  3. 5. cold-blooded
  4. 7. rasping tongue
  5. 8. helps keep fishes depth
  6. 10. tail fin
  7. 11. fish having thin fins
  8. 12. similar to stingray