Question

The group of animals whose coelomic cavity is blood filled is
А. Mollusca
B. Nematoda
C. Arthropoda
D. Reptilia

Answer 1

Hint: Coel represents the presence of cavity. Haem represents the haem part of haemoglobin that is present in the Red blood cell. Haemocoel is defined as the blood containing body cavity. Other kinds of body cavities include Pseudocoelomates and acoelomates.

Complete Answer:
Haemocoel is the body cavity that remains filled with blood which starts 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.

Now let us gather information about given options:
(А) Mollusca: Mollusca are the animals that contain body cavities. Their body cavity is filled with blood. It helps in the circulation of blood throughout the body.
Nematoda: Nematodes contain some 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 acoelomates.
Arthropoda: It is the largest phylum in the animal world. Though molluscs also possess haemocoel but these are the first kingdoms to possess such cavities. So, our correct answer is arthropods.
Reptilia: They do not have any distinction in their thorax and abdomen. Instead of this they contain body cavity but their cavity is not filled with blood. So, they are not schizocoelomates.

Hence the correct answer is option C.

Note: A body cavity is particularly named as coelom which is found in the arthropods. Inside the coelom, organs can show movement 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.