Question

In Amphioxus, the circulatory system is
A. Closed
B. Without heart
C. without respiratory pigment
D. All of the above

Answer 1

Hint: Circulatory system is also called a vascular system, and the blood in this system helps to transport respiratory gases, nutrients, it helps in fighting diseases, and helps in the body stabilization, and helps in body homeostasis.

Complete answer:
In invertebrates and many vertebrates, the type of circulatory system is closed.
A closed Circulatory system is confined within a series of vessels such as arteries, veins, and capillaries.
The pattern of the amphioxus circulatory system is blood moves forward ventrally and backward dorsally.
They contain well-defined contractile vessels, vascular spaces, or sinuses, within the connective tissue matrix.
In this amphioxus circulatory system, the heart is absent and the blood is pumped by the contractile vessels.
Contractile vessels have discontinuous endothelial lining, and it is rested on the basal lamina, And enclosed by a simple layer of myoepithelial cells.
They also contain arterial plexus which is continuous plexus along the whole length of the dorso ventral wall of the body.
Along with the circulation, this arterial plexus has one other supplementary function called respiration.
In this amphioxus circulatory system, as the blood is circulated within the vessels, this type of circulation is called as closed, and they lack the red corpuscles and respiratory pigment, and the blood is colorless.
Blood is found not only in the blood vessels but also in the spaces.
The main function of the circulatory system is to transport food and excretory wastes.
The heart is absent in the amphioxus circulatory system, pumping is done by contractile vessels.

So from the all above explanation, all the above is the correct answer.

Note: So in the amphioxus circulatory like branchiostoma, Most blood vessels generally look similar, but due to their similarities with blood vessels of vertebrates they are called arteries or veins. The principal arteries have muscular walls and only the dorsal aorta has an endothelial lining.