Question

In which group of animals, body cavity is filled with blood?
A) Nematoda
B) Arthropoda
C) Amphibians
D) None of the above

Answer 1

Hint: They are the invertebrate animals having highly developed sense organs, segmented bodies, exoskeleton. They also possess a ventral nervous system with bilateral symmetry.
Examples are millipedes, insects, centipedes etc.

Complete Answer:
- Arthropods have a body cavity that is called a coelom which is a membrane-lined cavity between the gut and the body wall that fits the internal organs.
- Coelom is the body cavity in most of the animals. In Arthropoda, the body cavity is filled with the blood and this is called haemocoel.
- Haemocoel is the body cavity that is filled with blood which arises in the embryonic mesoderm and it is an enlarged blastocoel and acts as a hydrostatic skeleton. This cavity develops in molluscs, arthropods and annelids with the splitting of mesoderm. It is called schizocoelom and this is filled with blood.

Thus, the correct answer is option B. i.e. Arthropoda.

Additional information: Nematodes have a space between the body wall and the digestive tract and are not lined with tissue. So, it is not considered as the true coelom. They are the phylum of worms which includes free-living non parasitic species. Amphibians are the small vertebrates that are found in moist environments. They have special glands that produce useful proteins.

Note: A body cavity is called coelom which is found in the arthropods. Inside the coelom, organs can move freely, grow independently and it protects them from the shocks. Arthropods have an open circulatory system which consists of a heart and blood filled called a haemocoel.