Gills can be both internal and external, depending on the animal.
Internal vs. External Gills:
The location of gills is a significant factor in how they function and how they are protected.
External Gills
- Definition: External gills are structures that project outwards from the body of an aquatic animal. These gills directly interact with the water to exchange gases.
- Protection: These gills lack the protection of a body cavity. They are vulnerable to damage and predation.
- Example: Axolotls are amphibians with external gills. You can see them clearly as feather-like structures protruding from their heads.
Internal Gills
- Definition: Internal gills are located inside the body of the animal. These gills are within a protective cavity and are part of a more complex system.
- Protection: Internal gills are protected by the body, making them less vulnerable than external gills.
- Example: Most fish species have internal gills, which are protected by the operculum (a bony plate that covers the gills). Sharks, while not having a bony operculum, have gill slits, which are openings that allow water to pass over the internal gills.
Table: Gills - Internal vs. External
| Feature | External Gills | Internal Gills |
|---|---|---|
| Location | Outside the body | Inside the body |
| Protection | Minimal, vulnerable to damage | Protected by body structures |
| Example Animals | Axolotls, some larval amphibians | Most fish, sharks (via gill slits) |
In summary, whether gills are internal or external is determined by the location of the gills. External gills protrude from the body and are exposed to the environment, whereas internal gills are enclosed within a body cavity for protection.
