Question

Living vertebrates can be divided into two major clades. Select the appropriate pair.

(A) the chordates and the tetrapods

(B) the urochordates and the cephalochordates

(C) the cyclostomes and the gnathostomes

(D) the marsupials and the eutherians

Short answer

(A) The statement“the chordates and the tetrapods” is false.

(B) The statement “the urochordates and the cephalochordates” is false.

(C) The statement “the cyclostomes and the gnathostomes” is true.

(D) The statement “the marsupials and the eutherians” is false.

Step-by-step solution

Phylogeny

In biological science, the term phylogeny is used for describing the diagrammatic representation of evolution and the relationship between the ancestors and descendent groups. The clade is a part of the phylogeny, which comprises an ancestor and all its lineages.

Explanation of option ‘(A)’

The chordate is a phylum of the Deuterostomia clade, and it contains three sub-phyla, all having notochords and nerve cords (hollow and dorsal). The tetrapods are organisms belonging to the sub-phylum vertebrate.

Thus, all the vertebrates are a lineage of the phylum chordate.

Therefore, the given statement is false.

Explanation of option ‘(B)’

The urochordates and cephalochordates are two of the three sub-phyla of the main phylum chordate. These are invertebrate organisms that have more resemblance to vertebrate organisms as compared with other invertebrate groups.

Thus, the groups mentioned in this option are descendants of the phylum chordate.

Therefore, the given statement is false.

Explanation of option ‘(C)’

The sub-phylum Vertebrata is further sub-divided into different groups and classes based on their structural and physiological differences. The two major clades are cyclostomes (vertebrates that lack jaws) and gnathostomes (vertebrates that have jaws).

Thus, the presence or absence of jaws divides vertebrates into two clades; cyclostomes and gnathostomes.

Therefore, the given statement is true.

Explanation of option ‘(D)’

Mammals constitute the vertebrate class Mammalia and these organisms also display several differences. Marsupials are mammals in which the offspring are raised within an externally placed pouch in the female body.

In contrast, the eutherians are placental mammals and lack any external body pouch.

Thus, the marsupials and eutherians are groups of the class Mammalia.

Therefore, the given statement is false.