What is suggested by the similarity of early embryos of different species of vertebrates?
a. recent common ancestryb. evolution from a distant common ancestorc. no evolutionary relationship between the groupsd. similar environments in the past

The correct answer is - b. evolution from a distant common ancestor.

The early embryos very often do not resemble the physical appearance of their parents. They tend to have an appearance and features that look much more like some other species or group of animals. That slowly changes though as the embryo matures, gradually taking the shape and physical appearance of its parents.

The early embryos do not have the tendency of relatively quick change as the evolution goes on, but instead, they can have the same features as some very distant ancestor, even from tens of millions of years ago. This suggest that the parents of the embryo, as well as the embryo itself has a distant common ancestor with other species that have that appearance.

We can take the birds as an example. The early embryos of the birds have tails, instead of beak, they have a jaw with tiny sharp teeth, and their appearance is very reptilian. In fact, the birds are related with the reptilians, though that connection dates way back in the geological past.

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.