A) open
B) reduced
C) closed
D) absent
Correct Answer: A
Solution :
Blood vascular system is a circulatory system containing a special body fluid (blood) and a pumping organ or heart. It occurs in vertebrates and higher invertebrates (from annelids onwards). The blood vascular system in hemichordates is simple and open type. It includes a dorsal heart and two longitudinal vessels (one dorsal and one ventral). In open blood vascular system, blood does not remain confined to blood vessels. It is less efficient and found in leech, prawns, crabs, insects, spiders. In chordates, closed circulatory system is found except in hemichordata or stomochordata (eg, Herdmanid) where, open circulatory system occurs.
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