Question

Which one of the following is a protochordata?
A. Amphioxus
B. Lamprey
C. Labeo
D. Exocoetus

Answer 1

Hint: The protochordates have a hollow dorsal nerve cord, gill slits, and a stiff supporting rod, the notochord. The protochordates differ chiefly from the vertebrates in not having a backbone.

Complete Answer:
- Protochordates are an informal group of species primarily referred to as invertebrate animals closely related to vertebrate animals. This group consists of Phylum Hemichordata and Subphylum Urochordata and Cephalochordata. They are distinguished by the appearance of a notochord at some point of their lives.
- Phylum Chordata is categorized into three subphyla: Urochordata or Tunicata, Cephalochordata and Vertebrata. Subphylum Urochordata and Cephalochordata are often referred to as protochordates and are exclusively marine.
- Amphioxus, also known as lancelets, in the Cephalochordata Subphylum, is a marine species in the Chordata group. They are small aquatic species widely present in the coastal waters of colder areas of the world and less frequently found in temperate waters.
- Lamprey belongs to subphylum vertebrata, class cyclostomata which are categories of jawless fishes. Class Osteichthyes of phylum vertebrata includes both marine and freshwater fishes with bony endoskeleton. Their body is streamlined. Labeo is included in Osteichthyes. Exocoetus represents a genus of bony, flying fish.

Thus, the correct answer is option A i.e., Amphioxus.

Note: Notochord is a long rod-like support system that extends around the back of the animal dividing the nerve tissue from the gut. It offers a place for muscles to attach for convenience of movement. Protochordates do not have a proper notochord present at all times of their life or for the full lifespan of the animal.