Which of the following is not a characteristic feature of phylum mollusca?

Options

A. They are bilaterally symmetrical, triploblastic and coelomate animals
B. Unsegmented animals
C. They are usually dioecious and oviparous with indirect development
D. Respiratory organs are feather like gills in all molluscs and are present in visceral hump,help in respiration and excretion.

Explanation

To determine which statement is not a characteristic feature of phylum Mollusca, we will analyze each of the four statements provided:

1. **Statement 1**: "They are bilaterally symmetrical, triploblastic, and coelomate animals."
- **Analysis**: This statement is true. Molluscs exhibit bilateral symmetry, possess three germ layers (ectoderm, mesoderm, and endoderm), and have a coelom (body cavity).

2. **Statement 2**: "These are unsegmented animals."
- **Analysis**: This statement is also true. Molluscs are indeed unsegmented, meaning their bodies are not divided into segments like those of annelids.

3. **Statement 3**: "They are usually dioecious, oviparous with indirect development."
- **Analysis**: This statement is true as well. Most molluscs are dioecious (having separate sexes), oviparous (laying eggs), and undergo indirect development, which includes a larval stage.

4. **Statement 4**: "Respiratory organs are feather-like gills in all molluscs and are present in the visceral hump. They help in respiration and excretion."
- **Analysis**: This statement is false. While molluscs do have feather-like gills (called ctenidia), these are located in the mantle cavity, not the visceral hump. The visceral hump is part of the mollusc's body that contains the internal organs.

**Conclusion**: The incorrect statement is Statement 4, as it misplaces the location of the respiratory organs.

**Final Answer**: Statement 4 is not a characteristic feature of phylum Mollusca.

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