1. http://biology.kenyon.edu/HHMI/Biol113/eukaryoticcells.htm
2. http://en.wikipedia.org/wiki/Gastrulation
3. https://www.boundless.com/biology/textbooks/boundless-biology-textbook/introduction-to-animal-diversity-27/features-used-toclassify-animals-163/animal-characterization-based-on-body-symmetry-634-11856/
4. http://www.iaszoology.com/symmetry-2/
5. http://www.diffen.com/difference/Invertebrate_vs_Vertebrate
6. http://classic.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Nematoda/
7. http://www.ucmp.berkeley.edu/porifera/porifera.html
8. http://www.ucmp.berkeley.edu/cnidaria/cnidaria.html
9. http://classic.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Platyhelminthes/
10. http://bio.rutgers.edu/~gb102/lab_2/307am-mollusca.html
11. http://www.earthlife.net/inverts/annelida.html
12. http://www.earthlife.net/inverts/arthropoda.html
13. http://www.earthlife.net/inverts/echinodermata.html
14. http://www.encyclopedia.com/topic/Agnathans.aspx
15. http://www.untamedscience.com/class/chondrichthyes/
16. http://www.newworldencyclopedia.org/entry/Osteichthyes
17. http://www.shsu.edu/~bio_mlt/AMPHIBIA.html
18. http://www.darwinsgalapagos.com/animals/reptilia_reptiles.htm
19. http://animaldiversity.org/accounts/Aves/
20. http://classic.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Chordata/Vertebrata/Mammalia/
21. http://en.wikipedia.org/wiki/Sponge
22. http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch7invertebrates/Invertwp/invert_wp_05/cnidaria/miles1/Classification.htm
23. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-turbellaria.html
24. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-trematoda.html
25. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-cestoda.html
26. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-monogenea.html
27. http://www.ehow.com/list_7353335_classes-nematodes.html
28. http://www.nhptv.org/wild/merostomata.asp
29. http://www.angelfire.com/mo2/animals1/arthropod/arachnid.html
30. http://www.seawater.no/fauna/arthropoda/Pycnogonida.html
31. http://www.ucmp.berkeley.edu/echinodermata/asteroidea.html
32. http://www.ucmp.berkeley.edu/echinodermata/ophiuroidea.html
33. http://www.ucmp.berkeley.edu/echinodermata/echinoidea.html
34. http://www.ucmp.berkeley.edu/echinodermata/crinoidea.html
35. http://www.ucmp.berkeley.edu/echinodermata/holothuroidea.html
2. http://en.wikipedia.org/wiki/Gastrulation
3. https://www.boundless.com/biology/textbooks/boundless-biology-textbook/introduction-to-animal-diversity-27/features-used-toclassify-animals-163/animal-characterization-based-on-body-symmetry-634-11856/
4. http://www.iaszoology.com/symmetry-2/
5. http://www.diffen.com/difference/Invertebrate_vs_Vertebrate
6. http://classic.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Nematoda/
7. http://www.ucmp.berkeley.edu/porifera/porifera.html
8. http://www.ucmp.berkeley.edu/cnidaria/cnidaria.html
9. http://classic.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Platyhelminthes/
10. http://bio.rutgers.edu/~gb102/lab_2/307am-mollusca.html
11. http://www.earthlife.net/inverts/annelida.html
12. http://www.earthlife.net/inverts/arthropoda.html
13. http://www.earthlife.net/inverts/echinodermata.html
14. http://www.encyclopedia.com/topic/Agnathans.aspx
15. http://www.untamedscience.com/class/chondrichthyes/
16. http://www.newworldencyclopedia.org/entry/Osteichthyes
17. http://www.shsu.edu/~bio_mlt/AMPHIBIA.html
18. http://www.darwinsgalapagos.com/animals/reptilia_reptiles.htm
19. http://animaldiversity.org/accounts/Aves/
20. http://classic.sidwell.edu/us/science/vlb5/Labs/Classification_Lab/Eukarya/Animalia/Chordata/Vertebrata/Mammalia/
21. http://en.wikipedia.org/wiki/Sponge
22. http://w3.shorecrest.org/~Lisa_Peck/MarineBio/syllabus/ch7invertebrates/Invertwp/invert_wp_05/cnidaria/miles1/Classification.htm
23. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-turbellaria.html
24. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-trematoda.html
25. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-cestoda.html
26. http://www.infoplease.com/encyclopedia/science/platyhelminthes-class-monogenea.html
27. http://www.ehow.com/list_7353335_classes-nematodes.html
28. http://www.nhptv.org/wild/merostomata.asp
29. http://www.angelfire.com/mo2/animals1/arthropod/arachnid.html
30. http://www.seawater.no/fauna/arthropoda/Pycnogonida.html
31. http://www.ucmp.berkeley.edu/echinodermata/asteroidea.html
32. http://www.ucmp.berkeley.edu/echinodermata/ophiuroidea.html
33. http://www.ucmp.berkeley.edu/echinodermata/echinoidea.html
34. http://www.ucmp.berkeley.edu/echinodermata/crinoidea.html
35. http://www.ucmp.berkeley.edu/echinodermata/holothuroidea.html