Based on the tree in Figure 32.11, which statement is true?


A. The animal kingdom is not monophyletic.
B. The Acoela are more closely related to echinoderms than to annelids.
C. Sponges are basal animals.
D. Bilaterians do not form a clade.

Verified step by step guidance

1. Identify the key terms in each statement and understand their meanings. Monophyletic refers to a group of organisms that consists of all the descendants of a common ancestor. A clade is a group of organisms believed to comprise all the evolutionary descendants of a common ancestor.
2. Examine the tree provided in Figure 32.11 to determine the relationships between the groups mentioned in each statement. Look for the common ancestors and the branching patterns that include or exclude certain groups.
3. Assess statement A by checking if the animal kingdom includes all descendants from a common ancestor without excluding any descendant group, which would indicate if it is monophyletic or not.
4. Evaluate statement B by tracing the lineage from Acoela to echinoderms and annelids on the tree to see which group Acoela shares a more recent common ancestor with.
5. Verify statement C by determining if sponges are placed at the base of the tree, which would suggest they are basal, meaning they diverge earlier than other groups in the evolutionary history of animals.

Key Concepts

Monophyly

Monophyly refers to a group of organisms that includes an ancestor and all its descendants, forming a complete branch on the tree of life. In contrast, a paraphyletic group includes an ancestor but not all its descendants, while a polyphyletic group consists of unrelated organisms that do not share a recent common ancestor. Understanding monophyly is crucial for evaluating the evolutionary relationships depicted in phylogenetic trees.

Basal Animals

Basal animals are those that diverged early in the evolutionary history of the animal kingdom and are considered to be more primitive or ancestral. Sponges, for example, are often classified as basal animals because they lack true tissues and organs, representing a fundamental branch of the animal lineage. Recognizing basal animals helps in understanding the evolutionary development of more complex organisms.

Bilaterians

Bilaterians are a major group of animals characterized by bilateral symmetry, meaning they have a distinct front and back, as well as a top and bottom. This group includes most animal phyla, such as arthropods, mollusks, and vertebrates. The concept of bilaterians is essential for understanding the evolutionary relationships and classification of animals, particularly in distinguishing them from other groups like radial animals.