Which one is a hypothetical ancestor of existing sponges ?

Options

A. Leucosolenia
B. Olyanthus
C. Grantia
D. Hyalonema

Answer

To determine the hypothetical ancestor of existing sponges, we need to analyze the options provided and understand the characteristics of each.

### Step-by-Step Solution:

1. **Understanding Hypothetical Ancestors**:
- A hypothetical ancestor is an assumed ancestor that is considered to have a simple structure. In the context of sponges, we are looking for the simplest form that could represent the ancestor of all sponges.

2. **Analyzing the Options**:
- **Leukosolenia**: This sponge belongs to the phylum Porifera and the class Calcarea. It has a simple canal system known as the Asconoid canal system.
- **Olynthus**: This sponge is also part of the phylum Porifera and is recognized for having a very simple structure. Its canal system is also Asconoid. According to Haeckel's hypothesis, Olynthus is considered the simplest form and thus the hypothetical ancestor of sponges.
- **Grantia**: Another sponge in the class Calcarea, but it is not typically identified as the simplest ancestor.
- **Hyalonema**: This sponge belongs to the class Hexactinellida and has a more complex structure compared to the others.

3. **Identifying the Correct Answer**:
- Based on the analysis, Olynthus is recognized as the hypothetical ancestor of existing sponges due to its simple structure and canal system. It is supported by Haeckel's hypothesis, which posits that Olynthus represents the simplest form of sponge.

### Conclusion:
The hypothetical ancestor of existing sponges is **Olynthus**.

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