Correct Option
The correct option is Arthropods and molluscs.
Explanation
Circulatory systems in the animal kingdom are primarily classified into two types based on how blood is transported:
- Open Circulatory System: Blood is pumped by the heart into large vessels that open into body cavities (sinuses). The tissues and cells are directly bathed in blood (hemolymph).
- Closed Circulatory System: Blood circulates exclusively within a closed network of blood vessels (arteries, veins, and capillaries). This system allows for more efficient transport and higher pressure.
Analysis of Options
- Arthropods and molluscs Arthropods and molluscs: Correct. Arthropods (e.g., insects, crustaceans, spiders) possess an open circulatory system where the hemolymph fills the body cavity (hemocoel). Similarly, most molluscs (e.g., snails, clams) have an open system, although cephalopods (like squids and octopuses) are an exception with a closed system.
- Annelids and chordates Annelids and chordates: Incorrect. Annelids (e.g., earthworms) and Chordates (which include all vertebrates) possess a closed circulatory system. This allows for efficient transport of nutrients and gases required for their physiology.
- Fishes and amphibians Fishes and amphibians: Incorrect. Both groups belong to the phylum Chordata (Vertebrata). They possess a closed circulatory system with a heart that pumps blood through distinct vessels.
- Birds and mammals Birds and mammals: Incorrect. These are warm-blooded vertebrates with high metabolic demands, necessitating a highly efficient closed circulatory system to transport oxygen and nutrients rapidly.
Key Takeaway: Generally, Arthropods and non-cephalopod Molluscs exhibit an open circulatory system, whereas Annelids and Chordates (vertebrates) exhibit a closed circulatory system.