Question

Animals whose phylum contains an open circulatory system.
A. Arthropoda
B. Annelida
C. Hemichordata
D. Both A and C.

Answer 1

The blood circulation which is not closed within the veins and arteries, instead it opens up in a body cavity called hemocoel is known as the open circulatory system. The open circulatory system comprises hemolymph instead of blood.

Complete answer:

Arthropoda:
i) Arthropoda is the largest phylum of the animal kingdom. It comprises 80% of the total known species.
ii) Arthropoda comprises segmented body paired legs with joints and exoskeleton.
iii) Body segmentation involves the head, thorax, and abdomen
iv) Arthropods have an open circulatory system.
v) Chitin is the key material of the exoskeleton.
vi) Arthropods comprise the complete digestive system.
Annelids:
i) Bilaterally symmetrical body.
ii) Length of the body varies between 1mm to 3m
iii) A cavity is found between the outer body wall and gut, which is known as a coelom. The coelom is responsible for storing the gametes and locomotion.
iv) An external cuticle is found at the outside of the body wall.
v) The circulatory system is a closed type
Hemichordata:
i) Hemichordata involves a bilaterally symmetrical body.
ii) The body is composed of proboscis, collar, and trunk.
iii) It comprises a true coelom.
iv) The respiratory system is Gill.
v) Hemichordata has an open circulatory system.

Note:
Hemolymph is the fluid that is found within the hemocoel. In the open circulatory system body fluid or hemolymph gets direct contact with the body tissue. Hemolymph is composed of hemocytes. Hemocytes are involved in the immune system of the invertebrates.