Biology · Animal Kingdom · NEET
NCERT says it directly: in the OPEN type, blood is pumped out of the heart and the cells and tissues are directly bathed in it. In the CLOSED type, blood is circulated through a series of vessels of varying diameters — arteries, veins and capillaries — so it never leaves the tubes. That single point (cells bathed directly vs blood stays in vessels) is the whole difference NEET wants.
Arthropods (like cockroach, prawn, insects) and most molluscs (like snails) have an open circulatory system. Their blood flows into large open spaces in the body called the haemocoel. Remember: the two biggest phyla with open type are Arthropoda and Mollusca.
Annelids (like earthworm and leech), some molluscs (like octopus and squid), Echinoderms are debated, and all chordates (fishes, amphibians, reptiles, birds, mammals — including humans) have a closed circulatory system. Blood stays inside vessels the whole time. This is why NEET lists 'closed circulatory system' as a chordate feature.
Human circulation is CLOSED. Our blood always travels inside blood vessels (arteries, capillaries, veins) and is never in direct contact with body cells — exchange happens across thin capillary walls. All chordates, including humans, are closed type. This is a common trap, so lock it in.
The haemocoel is the body cavity filled with blood in animals with an open circulatory system. Since blood is pumped into these open spaces, the organs sit inside blood directly. The word 'haemocoel' is a clue that the animal (like an arthropod) has an OPEN circulatory system.
Because blood moves inside vessels under higher, controlled pressure, it can be directed quickly to the exact organ that needs it. In an open system, blood flows slowly through open spaces with low pressure, so distribution is less precise. NEET may frame this as 'closed = faster, controlled flow'.
Select the correct statements with reference to chordates. A. Presence of a mid-dorsal, solid and double nerve cord. B. Presence of closed circulatory system. C. Presence of paired pharyngeal gill slits. D. Presence of dorsal heart. E. Triploblastic pseudocoelomate animals.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
No. MOST molluscs (like snails and clams) have an open circulatory system, but cephalopods such as octopus and squid have a closed circulatory system. So 'Mollusca = open' is only mostly true, not always.
The earthworm (Phylum Annelida) has a CLOSED circulatory system. Blood stays inside vessels. This is a favourite NEET point because it contrasts with arthropods, which are also 'worms/insects' to a beginner but are OPEN type.
Arteries, veins and capillaries. NCERT specifically states blood is circulated through a series of vessels of varying diameters. If a question mentions capillaries, it is describing the closed type.
No. All chordates have a closed circulatory system. Open circulation is limited to invertebrates like arthropods and most molluscs. If the animal is a chordate, the answer is always closed.
