Question

Cephalothorax is seen in organisms of phylum

• A. Platyhelminthes
• B. Aschelminthes
• C. Annelida
• D. Arthropoda

Answer 1

The correct option is D Arthropoda

Phylum Arthropoda includes all the organisms that have jointed appendages. Their body consists of the head, thorax and abdomen. In some arthropods, the head and thorax are fused and there is no distinction between the head and thorax. This condition is known as cephalothorax. It is observed in crabs, prawns etc.

Organisms belonging to phylum Platyhelminthes and all phyla following it have bilateral symmetry. Bilateral symmetry is often associated with cephalization, though not always. Cephalization is the phenomenon of concentration of nervous tissues and sensory organs in the head of the organism. Hence, organisms in phylum Platyhelminthes and onwards have a structure called head. But Platyhelminthes, Aschelminthes and Annelids are devoid of thorax.