This group of animals is characterized by a transition to bilateral symmetry.Multiple choice question.EumetazoaParazoaBilateria

1. Break Down the Problem

We need to identify which group of animals is characterized by a transition to bilateral symmetry. The options given are Eumetazoa, Parazoa, and Bilateria.

2. Relevant Concepts

• Eumetazoa: This clade is comprised of all animals except for Porifera (sponges). Eumetazoans exhibit true tissues and are mostly characterized by having symmetry, including bilateral symmetry.
• Parazoa: This term refers mainly to sponges (e.g., Porifera) that do not have true tissues and are asymmetrical or exhibit radial symmetry.
• Bilateria: This group includes all animals with bilateral symmetry, which allows for a distinct front and back, leading to more complex body plans.

3. Analysis and Detail

• Eumetazoa: Evolved after Parazoa and are characterized by the presence of tissues and symmetry. Bilateral symmetry is more commonly found in more evolved Eumetazoans.
• Parazoa: Comprises animals like sponges that do not show bilateral symmetry and lack organized tissues.
• Bilateria: Refers to animals that exhibit bilateral symmetry as a significant characteristic.

4. Verify and Summarize

After analyzing the characteristics of each group, it is evident that Bilateria is defined specifically by the presence of bilateral symmetry.

Final Answer

The correct answer is Bilateria.