Which one of the following group of animals is bilaterally symmetrical and triploblastic?

Aschelminthes 

The correct answer is Option (1)- Aschelminthes
Animal are classified on the basis of symmetry of body plan and germ layers if the body plan is made up of three germ layers called as triploblastic and if it made up of two germ layers called as diploblastic.

The body of the aschelminthes is circular in cross-section, hence, the name roundworms. They may be free living, aquatic and terrestrial or parasitic in plants and animals. Roundworms have organ-system level of body organisation. They are bilaterally symmetrical, triploblastic and pseudocoelomate animals. Alimentary canal is complete with a well developed muscular pharynx.

Ctenophores are biradially symmetrical and diploblastic, whereas some species are triploblastic. 

Sponges are asymmetrical and and diploblastic. 

Coelenterates are radially symmetrical and diploblastic.