Question

In which group of animals, the coelom is filled with blood?
A.Arthropoda
B.Annelida
C.Nematoda
D.Echinodermata

Answer 1

Hint: The main cavity that is present between the body wall and the alimentary canal is known as the coelom and this cavity is filled with fluid known as the coelomic fluid.

Complete answer:
1.Based on the presence or absence of coelom animals can be classified as acoelomate, pseudocoelomate, and coelomate.
2.Arthropods are acoelomate animals and it has an open circulatory system where the blood from the heart is transported to the different organs through the body cavity known as a coelom and it returns to the heart through certain openings known as Ostia.
3.The blood in the arthropods is known as the Hemolymph and this blood is present in the coelom as there are no arteries and veins to carry the blood in the arthropods.

Option A: Arthropods have an open circulation system and hence the body cavity coelom is filled with blood known as hemolymph. Therefore, this is the correct option.

Option B: Annelids have a closed circulatory system. Therefore, this is the incorrect option.

Option C: Nematodes do not possess any circulatory system and the oxygen in the nematodes is supplied by diffusion. Therefore, this is the incorrect option.

Option D: In Echinoderms, there is a special canal system that is responsible for circulation and other functions in echinoderms. Therefore, this is the incorrect option.

Hence, the correct answer is option (A)

Note: Due to the absence of blood vessels in arthropods, their blood gets mixed up with the interstitial fluid and all the organs in arthropods are suspended in the hemolymph and the cavity where the hemolymph is present is known as the hemocoel and the energy consumption in the open circulatory system is comparatively less than the closed circulation system.