Q.Which of the following does not have an open circulatory system?

Step 1. Recall the two types of circulatory systems. In a closed circulatory system, blood is always confined within vessels (arteries, veins, capillaries), so it never directly bathes the body tissues. In an open circulatory system, the heart pumps a fluid called haemolymph into open sinuses (a haemocoel), where it bathes tissues directly before slowly returning to the heart.

Step 2. Classify each option. Frog — a vertebrate with a well-developed closed circulatory system (three-chambered heart, arteries, veins, capillaries). Pigeon — a vertebrate with a closed, double circulatory system (four-chambered heart). Earthworm — an annelid; despite being an invertebrate, it has a closed circulatory system with a dorsal and a ventral blood vessel joined by lateral hearts (aortic arches) and capillaries in each segment. Cockroach — an arthropod (insect); arthropods characteristically have an open circulatory system, with a dorsal tubular heart pumping haemolymph into the haemocoel that surrounds the internal organs directly. …

Classify each listed animal by its phylum (Chordata/vertebrate, Annelida, or Arthropoda) and recall that only arthropods have an open circulatory syste …

• Assuming all invertebrates have an open circulatory system, and so wrongly picking the earthworm as having one
• Confusing the earthworm's segmental 'hearts' (aortic arches) with an open system just because it lacks a single centralized heart like vertebrates …