Hint:Animals with three pairs of legs are called insects. Body of insects is divided into three segments. They are head, thorax and abdomen. They belong to a phylum which is the largest phylum in kingdom animalia.
Complete answer: We know that the largest phylum in kingdom animalia is Arthropoda. The word meaning of the term Arthropoda is jointed appendages. Animals in this phylum have jointed appendages. Know that this phylum includes the class insecta which are the animals with three pairs of legs.
Arthropoda consists of animals that have their body covered by a chitinous exoskeleton which is for protection. Sensory organs of these animals include eyes, antennae and statocysts. Examples of insects are beetles, fly, dragonfly, cockroach etc.
Annelida is the phylum that includes earthworms. The Bodies of these organisms are metamerically segmented and hence the name Annelida. Neries and Hirudinaria are the other examples of phylum Annelida.
Echinodermata includes marine organisms that have an endoskeleton which is made up of calcareous ossicles. Starfish belongs to this phylum.
Mollusca is the second largest phylum of kingdom animalia. Know that these animals have a shell made up of calcium carbonate and an unsegmented body. Cuttlefish and pearl oysters belong to this phylum.
Hence the correct answer is option ‘A’.
Note:Chitinous exoskeleton of arthropods can be periodically removed and renewed. This process is known as moulting or ecdysis. Know that this process helps in growth and expansion of the body of these animals. Keep in mind that this exoskeleton made up of chitin also contains certain proteins and is hardened by calcium carbonate and calcium phosphate.