Classification Of Animals

In biology, symmetry refers to the arrangement of body parts around a central axis. Radial symmetry is a type of symmetry where body parts are arranged around a central point, like spokes on a wheel. This form of symmetry is common in certain animal phyla, mainly those in aquatic environments.

Let's examine the phyla mentioned in the options to determine which one does not exhibit radial symmetry in adults:

1. Hemichordata: Members of this phylum, such as acorn worms, exhibit bilateral symmetry in their adult forms, not radial symmetry.
2. Coelenterata: This term often refers to Cnidaria, which includes jellyfish and corals, known for their radial symmetry.
3. Echinodermata: This group includes starfish and sea urchins, which show radial symmetry as adults.
4. Ctenophora: Also known as comb jellies, these organisms are characterized by their radial symmetry.

Based on this analysis, radial symmetry is NOT found in adults of the phylum Hemichordata.

Annelids and arthropods: Bilateral symmetry: Correct. Both phyla exhibit bilateral symmetry.

Sponges: Acoelomates: Correct. Sponges lack a coelom (body cavity).

Coelenterates and Ctenophores: Radial symmetry: Correct. Both phyla exhibit radial symmetry.

Platyhelminthes: Diploblastic organisation: Incorrect. Platyhelminthes (flatworms) are triploblastic, meaning they have three germ layers (ectoderm, mesoderm, and endoderm). Diploblastic organisms only have two germ layers (ectoderm and endoderm).

A. Chondrichthyes: Cartilaginous fishes, such as sharks (e.g., Carcharodon). A-II

B. Cyclostomata: Jawless fishes, such as hagfish (e.g., Myxine). B-III

C. Osteichthyes: Bony fishes, such as catfish (e.g., Clarias). C-I

D. Amphibia: Amphibians, such as caecilians (e.g., Ichthyophis). D-IV