Look at the diagram above. Two balloons filled with freshwater have been placed into a tank of freshwater. Balloon A floats near the surface, and balloon B sinks to the bottom. What is true about balloon A? *

organisms that lack symmetry are called asymmetrical and belong to phylum porifera/sponges.

organisms with specialized stinging cells belong to phylum cnidaria. stinging cells are called cnidoblast cells.

cnidarians show two morphological forms : polyp (sessile) and medusa (mobile)

filter feeding is observed in porifera members.  

alternation of generation is observed in coelenterata or cnidaria. there is alternation of asexual polyp form and sexual medusoid form. it is also referred as metagenesis.

where is the scientific experiment?

i think that is new experiments yield untrustworthy data and should be carefully considered, because you don't know what will happen with the experiments.

that is wrong, its not thymus.