The group of animals whose coelomic cavity is blood filled is

The correct option is C Arthropoda
A coelom can be defined as a cavity lined by an epithelium derived from mesoderm. Organs formed inside a coelom can freely move, grow, and develop independently of the body wall while fluid cushions and protects them from shocks. The circulatory system of arthropods consists of a heart, a few blood vessels and the blood-filled hemocoel. The coelom is much reduced in arthropods and is usually represented only by small spaces associated with the gonads and excretory system. The body cavity is a hemocoel.