Question

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

• A. Sponges
• B. Coelentrates (Cnidarians)
• C. Aschelminthes (round worms)
• D. Ctenophores

Answer 1

The correct option is C Aschelminthes (round worms)

• The Aschhelminthes group of animals, which are also known as the Nemathelminthes or Nematodes or Roundworms, are bilaterally symmetrical and triploblastic animals. Examples of roundworms are - Ascaris (the common Roundworm), Ancylostoma (the common Hookworm), Wuchereria (the Filarial worm), etc.
• The Sponges or the Poriferans are either radially symmetrical or with no symmetry and are diploblastic animals. Examples are - Scypha, Leucosolenia, Spongilla, Euplectella, etc.
• Coelenterate or Cnidarians are either radially symmetrical or biradially symmetrical and diploblastic animals. Examples are - Metridium (Sea Anemone), Aurelia (Jelly-Fish), Obelia (Sea-Fur), etc.
• Ctenophores, commonly known as the Comb Jellies have biradial symmetry. Regarding the number of germ layers, Ctenophores are a little controversial. Traditionally, these animals are considered to be diploblastic. But nowadays according to many, they are recognized as triploblastic animals with a mesenchymal middle layer. Examples are - Ctenoplana, Coeloplana, Velamen, etc.
• So, the correct answer is 'Aschelminthes (round worms)'