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Biology Question 109 – NEET-UG 2025

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While trying to find out the characteristic of a newly found animal, a researcher did the histology of adult animal and observed a cavity with presence of mesodermal tissue towards the body wall but no mesodermal tissue was observed towards the alimentary canal. What could be the possible coelome of that animal ?

Understand the different types of body cavities (coelom) based on their origin and lining by mesodermal tissue.

● Video Walkthrough
Step 1: Define Coelom Types✦ Active

A coelom is a fluid-filled body cavity. Animals are classified based on the presence and nature of their coelom. Acoelomates lack a body cavity. Pseudocoelomates have a body cavity that is not completely lined by mesoderm. Coelomates (eucoelomates) have a true coelom, which is completely lined by mesoderm.

Step 2: Analyze the Animal's Characteristics○ Expand

The researcher observed a cavity with mesodermal tissue towards the body wall but no mesodermal tissue towards the alimentary canal. This means the cavity is partially, but not fully, lined by mesoderm.

💡 Teacher's Secret Hint

Pay close attention to which parts of the cavity are lined by mesoderm and which are not.

Step 3: Match with Definition○ Expand

This description precisely matches the definition of a pseudocoelomate. In pseudocoelomates, the body cavity is derived from the blastocoel and is lined by mesoderm only on the outer side (towards the body wall), while the inner side (towards the alimentary canal) is lined by endoderm.

💡 Teacher's Secret Hint

Remember that schizocoelomates are a type of true coelomate, where the coelom is fully lined by mesoderm.

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