Question

Stomochord is found in
(A) Urochordata
(B) Hemichordata
(C) Cephalochordata
(D) Both A and B

Answer 1

Hint: Stomochord is an out pocket which arises from the roof of embryonic gut. It is found anterior to the pharynx. Stomochord is responsible for providing the support to the body. Notochord is present in advanced organisms such as chordates. Notochord and stomochord have the same function.

Complete answer:
Urochordata is the subclass of phylum chordata. Notochord is present in the larval tail in such organisms. Stomochord is not found in urochordates. That’s why “Urochordata” is an incorrect option.
Cephalochordata is the sub class of phylum chordata. The notochord is present from the head to tail in cephalochordata. Stomochord is not found in the cephalochordate. That’s why “Cephalochordata” is an incorrect option.
Hemichordata is the closest relative of chordate. It is thought that it is found in phylum chordata. But it is placed under non-chordata. Stomochord is an out pocket which arises from the roof of embryonic gut in hemichordates. It is endodermal in nature. It’s lumen opens into a pharynx. Stomochord is non-supportive in nature and it helps in locomotion.

Additional information:
Hemichordates are placed in chordate phylum. But hemichordates don’t have notochord in their body. That’s why hemichordates don’t fall in the chordate category. Now, hemichordates are not found in chordates. Hemichordates are exclusively marine. They have bilateral symmetry because the body can be divided into two equal halves by the plane which passes through the centre of the axis. The Hemichordate's body is divided into: proboscis, collar and trunk.

That’s why option b. “hemichordate” is a correct option.

Note:
Notochord and stomochord are different structures. Notochord is found in all chordates. Stomochord is found in the hemichordates only. This structure provides support to the body. Chordates don’t have stomochords. Because they are more advanced as compared to the chordates. They have notochord for supporting the body.