Question

In Figure 33.2, which two main clades branch from the most recent common ancestor of the eumetazoans?

(A) Porifera and Cnidaria

(B) Lophotrochozoa and Ecdysozoa

(C) Cnidaria and Bilateria

(D) Deuterostomia and Bilateria

Short answer

(A) The option “Porifera and Cnidaria” is false.

(B) The option “Lophotrochozoa and Ecdysozoa” is false.

(C) The option “Cnidaria and Bilateria” is true.

(D) The option “Deuterostomia and Bilateria” is false.

Step-by-step solution

Eumetazoa

Eumetazoa are diploblastic organisms that are the sister group of the phylum Porifera. This group consists of all organisms except sponges and other organisms that belong to the group Placozoa. They were found more than 600 million years ago.

Explanation of option ‘(A)’

Porifera is not a descendant of Eumetazoa because Porifera belongs to a different subkingdom than Eumetazoans. The subkingdom to which they belong is called Parazoa. However, Cnidaria is a descendent of Eumetazoa.

Thus, Porifera is the descendant of Parazoa, and Cnidaria is a descendant of Eumetazoa.

Therefore, the given option is false.

Explanation of option ‘(B)’

Lophotrochozoa and Ecdysozoa are the branched subgroup of Bilateria. These organisms are descendants of the metazoans but are not the most recent descendants because Bilateria is present in between.

Thus, Lophotrochozoa and Ecdysozoa are not recent descendants of Eumetazoans.

Therefore, the given option is false.

Explanation of option ‘(C)’

Cnidaria and Bilateria are recent common ancestors that are present in the phylogenetic tree right after the metazoans. Hence they have a recent ancestor called the eumetazoans.

Thus,Lophotrochozoa and Ecdysozoa are recent descendants of Eumetazoans.

Therefore, the given option is true.

Explanation of option ‘(D)’

Step 5: Explanation of option ‘(D)’