Which of the following is an example of the changes that take place in an ecosystem during secondary succession?

a. algae, grasses, and small plants grow on newly exposed rock over a long period of time.
b. organisms compete for resources, and those that are best fit to survive establish themselves as dominant species.
c. predation causes a population of prey to migrate to a new location in order to survive.
d. shrubs and trees regrow quickly in an area that has been burned during a forest fire.

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.