what are invertebrates , animals that have backbone, they dosen`t have backbone  , animals make toilet , animals do fart, what should we call the simplest gruop of invertebrattes , cats, echinoderms , sponges, worms, what is the main function of the sponges, stinging cell, parasitic organism , non of these, what are example of the echinoderms , starfish, jellyfish.

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