Earthworm respires through its moist skin.

Respiration is the process by which organisms take in oxygen and release carbon dioxide. Earthworms, being invertebrates, do not have lungs or gills like vertebrates to respire. Instead, they have a specialized respiratory system that allows them to exchange gases directly through their skin.

Here is a detailed explanation of how earthworms respire through their moist skin:

1. Moist Skin:
- The skin of an earthworm is thin, moist, and highly vascularized, meaning it has a rich network of blood vessels close to the surface.
- The moist skin allows for efficient gas exchange as oxygen from the surrounding environment can dissolve in the moisture on the skin surface and diffuse into the bloodstream.
- At the same time, carbon dioxide produced during cellular respiration can diffuse out of the bloodstream and be released into the environment.

2. Cutaneous Respiration:
- Earthworms primarily respire through a process called cutaneous respiration, which means respiration through the skin.
- The exchange of gases occurs across the epidermis, the outermost layer of the earthworm's body.
- The epidermis is permeable to gases, allowing oxygen and carbon dioxide to pass through.
- The respiratory gases diffuse across the skin's moist surface and enter or leave the bloodstream through the network of blood vessels.

3. Importance of Moist Skin:
- The moisture on the skin surface is crucial for respiration in earthworms.
- It helps to keep the skin moist and prevents it from drying out, which is essential for efficient gas exchange.
- Earthworms secrete mucus that keeps their skin moist and provides a protective layer.
- The mucus also aids in trapping oxygen from the environment and facilitates its diffusion into the bloodstream.

4. Adaptations for Efficient Respiration:
- Earthworms have a long, slender body with a high surface area to volume ratio, which maximizes the area available for gas exchange.
- They also have a thin body wall, allowing gases to diffuse easily across the skin.
- The extensive network of blood vessels near the skin's surface ensures a short diffusion pathway for gases.
- Earthworms often live in moist environments, such as soil or leaf litter, which helps maintain the moisture on their skin necessary for respiration.

In conclusion, earthworms respire through their moist skin via a process called cutaneous respiration. The thin and highly vascularized skin, along with the presence of moisture and mucus, allows for efficient exchange of gases, ensuring the earthworm's respiratory needs are met.