The final electron acceptor in aerobic respiration is

Oxygen

Explanation:

Oxygen as a molecule is an effective oxidizing agent; therefore it acts as an electron acceptor in the chemical reactions involved in aerobic reaction. In case of anaerobic respiration sulfate, nitrate and sulfur are used as electron acceptors.  

All these electron accepting molecules have high reduction potential and thus reduce itself in the entire process.  

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.