Question

Haemocoel is found in
A. Hydra
B. Cockroach
C. Earthworm
D. Snake

Answer 1

Invertebrates have haemocoel as their main body cavity where their organs lie bathed in blood as they consist of an open circulatory system. It is mostly found in insects belonging to arthropods and the mollusca family.

Complete answer:
Haemocoel is the body cavity present in which blood which is known as haemolymph flows freely without any vessels. This cavity is found in organisms which have an open circulatory system. Haemolymph that flows through haemocoel is a colourless fluid which is rich in plasma and haemocytes. Heart is a tube-like organ in such organisms which pumps blood into the haemocoel.
In the given option only cockroach belongs to arthropods and the others like Hydra belongs to the phylum Coelenterata/Cnidaria and they don’t have a specialised circulatory system as they get oxygen from the water they live in, Earthworm belongs to the phylum Annelida which and they have a closed circulatory system with a well-developed system of vessels and Snake belongs to Chordata and has a closed circulatory system without a haemocoel.

Hence, the correct answer is option (B).

Additional information:
-Haemolymph is colourless because of the lack of haemoglobin, the pigment responsible for carrying oxygen in most of the vertebrates. A similar molecule called haemocyanin (green colour) is present at the place of haemoglobin.
-Body cavity of Hydra is larger than haemocoel and is known as Coelenteron. It is also known as gastrovascular cavity.
-Body cavity called Coelom is present in earthworms and snakes too.

Note: Though Coelom and Haemocoel are found in different organisms but they have only one basic difference that coelom is found in all organisms including humans that have a closed circulatory system and haemocoel in those that have an open circulatory system.