Question

In Amphioxus, blood circulatory system is:

• A. Closed
• B. Without heart
• C. Without respiratory pigment
• D. All of above

Answer 1

The correct option is D All of above

Amphioxus possesses a closed haemal system; the anatomical distribution of the main vessels and the direction of flow of haemal fluid (backwards dorsally and forwards ventrally) are reminiscent of those in the vertebrate embryo.

Circulatory system does not have heart and consists on two circuits:

• the ventral circuit goes from caudal fin to head
• the dorsal, the other way around.

The circulatory liquid goes to pharynx fissures to become oxygenated and has amebocytes, but it has not respiratory pigments, so breathing takes places by diffusion.