Question

Which of the following blood vascular system is present in Hemichordata?
A. Open
B. Reduced
C. Closed
D. Absent

Answer 1

Hint: Hemichordates are a group of worm-like marine organisms that have an organ-system level of organization. These animals are non-chordates. They have a body cavity called hemocoel in which blood flows. The organs directly are in contact with oxygen and nutrients.

Complete answer:
Hemichordates are marine animals that have a worm-like body and are considered a sister group of echinoderms. They are also called acorn worms. They have a hollow neural tube which is the same as echinoderms. 130 known species of hemichordates exist. They are of great interest to scientists to study chordate development. They are mostly found in the deep sea. These animals usually live in the burrows, and some of them are detritivores. Some of them live in colonies and some of them are solitary living organisms. Their bodies have a muscular organization. The body is divided into three parts called an anterior proboscis, middle collar and posterior trunk. An example of hemichordates is Balanoglossus gigas. Like worms, the hemichordates have a body cavity called hemocoel. The blood flows openly in the hemocoel. Due to this, the organs bathe in the blood of hemichordates. Oxygen and nutrients are directly exchanged from blood to organs. The blood and interstitial fluid are not separated.
Hence, option A is the correct answer.

Note: Hemichordates differentiate from echinoderms as it lack the post-anal tail or notochord. These characters differentiate both groups. Some of the hemichordates consist of tentacles on the collar. The reproductive and digestive organs are enclosed in the trunk portion of the hemichordates.