Question

Members of which of the following phyla are bilaterally symmetrical and triploblastic?

• A. Aschelminthes
• B. ctenophores
• C. sponges
• D. coelenterates

Answer 1

The correct option is A

Aschelminthes

Phylum Aschelminthes includes the roundworms which are all triploblastic and bilaterally symmetrical. Examples include Ascaris, Wuchereria etc. Echinoderms such as the starfish are triploblastic and radially symmetrical (in the adult stage, but bilaterally symmetrical in the larval stages). Porifera includes the sponges, which do not have true tissues (and hence, cannot be either diploblastic or triploblastic) and are asymmetrical. Cnidarians such as the jellyfish and corals are diploblastic and radially symmetrical.