Elasmobranchs lack

Options

A. Gill slits
B. Operculum
C. Notochord
D. Placoid scales

Answer

**Step-by-Step Solution:**

1. **Understanding Elasmobranchs**: Elasmobranchs are a subclass of cartilaginous fish that include sharks and rays. They are characterized by their skeletons made of cartilage rather than bone.

2. **Identifying the Options**: The question provides four options:
- A) Gill slits
- B) Operculum
- C) Notochord
- D) Placoid scales

3. **Analyzing Each Option**:
- **Gill Slits**: These are openings that allow water to flow over the gills for respiration. All fish, including elasmobranchs, possess gill slits.
- **Operculum**: This is a bony flap that covers the gills in bony fish (Osteichthyes). Elasmobranchs do not have an operculum.
- **Notochord**: This is a flexible rod that provides support. It is present in all chordates, including elasmobranchs, either during embryonic development or in the adult stage.
- **Placoid Scales**: These are small, tooth-like structures on the skin of elasmobranchs that provide protection and reduce drag while swimming. They are present in elasmobranchs.

4. **Conclusion**: Since elasmobranchs lack an operculum, the correct answer to the question is **B) Operculum**.

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