Question

Which one of the following is a chordate but not a vertebrate?
(A)Scoliodon
(B)Salamander
(C)Amphioxus
(D)Snake

Answer 1

Hint: The characteristic feature of a vertebrate is that the spinal cord of these organisms is surrounded by cartilage or bones and if not they are considered to be invertebrates. Vertebrates include the majority of the phylum Chordata.

Complete answer:
From the given organisms, the Amphioxus is a chordate but not a vertebrate.
Amphioxus, commonly known as lancelet, is a marine fish like chordate that possesses a dorsal nerve cord which is not protected by bone but by a simple notochord made up of a cylindrical cell pattern, closely packed to form a toughened rod. Therefore, they are different from vertebrates and are not considered in that group.

Additional information:
Salamander belongs to the class amphibia of phylum Chordata and is a lizard-like organism with a slender body, blunt snout, short limbs, and a tail in both larvae and adults. They are vertebrate organisms.
Scoliodon is a requiem shark and belongs to the class Chondrichthyes of phylum Chordata. They possess an elongated, spindle-shaped body that is perfect for fast swimming. They are vertebrate organisms as well.
Snakes are very common carnivorous reptiles characterized by an elongated, legless body and belong to the class reptilia of phylum Chordata. They are also vertebrates.

Therefore, the correct answer is "Amphioxus".

Note: Although Amphioxus are not vertebrates, according to zoologists they give evolutionary insight into the origins of vertebrates. They are similar and possibly related to an extinct primitive chordate called pikaia. Due to their organ and organ system being similar to modern fish but in more of a primitive form, they are considered to provide a number of examples of possible evolutionary exaptation. Their genomes hold clues about the early evolution of vertebrates by several factors such as
-by comparing genes from lancelets with the same genes in vertebrates
-changes in gene expression, function, and numbers.