Question

In contrast to annelids the platyhelminths show

• A. radial symmetry
• B. presence of pseudocoel
• C. bilateral symmetry
• D. absence of body cavity

Answer 1

The Correct Option is D

The question revolves around comparing the anatomical features of two phyla: Annelida and Platyhelminthes. To understand the correct answer, we must examine the key characteristics of these phyla:

• Annelids (e.g., earthworms): These are coelomates, meaning they possess a true body cavity (coelom) that is fully lined with mesoderm.
• Platyhelminths (e.g., flatworms): These are acoelomates, which means they do not have a body cavity between the digestive tract and the outer body wall.

Let's analyze the given options:

• Radial symmetry: Platyhelminths do not exhibit radial symmetry; rather, they have bilateral symmetry.
• Presence of pseudocoel: This is incorrect as a pseudocoel is found in nemahelminths (roundworms), not in platyhelminths.
• Bilateral symmetry: Both annelids and platyhelminths show bilateral symmetry, so this is not a contrasting feature.
• Absence of body cavity: This option is correct since platyhelminths lack a body cavity, contrasting with annelids that have a coelom.

Therefore, the correct answer is the absence of body cavity.

This defining characteristic sets platyhelminths apart from annelids and establishes the primary contrast between the two groups.