Http://www.livescience.com/22537-skeletal-system.html
I thinks it's Genetics. I might be wrong tho
Answer:
Cnidarians represent a more complex level of organization than Porifera. They possess outer and inner tissue layers that sandwich a noncellular mesoglea. Cnidarians possess a well-formed digestive system and carry out extracellular digestion.
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Optical microscope.
Hope this helps.