For a given trait, the two genes of an allelic pair are not alike. an individual possessing this gene combination is said to be

The individual processing of the combination of two unalike pair of allelic genesis said to be heterozygous. Genes comes in different version which is called alleles. An individual is said to be heterozygous when it has two different alleles. The opposite to heterozygous is homozygous.

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.

the answer is golgi apparatus