Answer: Open circulatory system.
- A Closed circulatory system
- B Open circulatory system
- C No circulatory system
- D Double circulation only
Correct answer: B. Open circulatory system
Explanation: Arthropods have an open circulatory system in which blood (hemolymph) flows freely in body spaces (hemocoel) rather than being confined to vessels.
Moving across the animal phyla, body organisation becomes progressively more complex: from no symmetry and cellular organisation (Porifera) through radial/diploblastic (Cnidaria), bilateral/acoelomate (Platyhelminthes), pseudocoelomate (Nematoda), to a true coelom with full organ systems (Annelida and beyond).
Concept context
Phylum-level classification of the animal kingdom from Porifera to Chordata, based on body symmetry, coelom, and segmentation. One of the most example-heavy chapters for NEET.