Question

Animals producing natural pearls belong to
A. Echinodermata
B. Cyclostomata
C. Mollusca
D. Fishes

Answer 1

Hint:Mollusca is the second largest phylum of the animal kingdom. They are triploblastic, coelomic animals. Some species undergo torsion. These are the animals that produce pearls by their mantle layer.

Complete answer:
Mollusca is the second-largest animal phylum. Mollusks are triploblastic, coelomate (schizocoelic) organisms with organ system level of organization. They have bilateral symmetry, but some are asymmetrical due to torsion as they grow. They have a tube within the tube body plan.
The body is soft and unsegmented, divisible into the head with sensory tentacles, foot, and visceral hump( contain digestive tract and other visceral organs). The soft body is covered by a fleshy fold called mantle/pallium. The mantle cavity is present between the visceral hump and mantle.
Mantle secretes a calcareous shell(conchiolin matrix and calcite and aragonite) on its outer surface in some species.
Pinctada or the Pearl oyster produces the best quality of the pearl.
Echinoderms are the spiny skinned animals. They are exclusively marine, triploblastic, enterocoelomate animals with organ system level of organization.
Cyclostomata are jawless, marine vertebrates, which are mainly ectoparasites on some fishes.
Fishes ( Pisces) are aquatic gnathostome vertebrates, divided into two classes- Chondrichthyes and Osteichthyes.
So, the correct answer is option C. Mollusca.

Note:
In mollusks, respiration is carried out by feather-like gills(ctenidia) in the mantle cavity or pulmonary chamber. Gills also help in excretion. The digestive system is well developed. It contains a rasping organ called radula for feeding. The excretory organ is one or two pairs of kidneys. The nervous system consists of paired ganglia. They are usually dioecious and oviparous with indirect development.