The correct answer is option 'D' - Earthworm.

Explanation:
Respiration is the process of obtaining oxygen from the environment and releasing carbon dioxide. In most animals, respiration occurs through specialized respiratory organs such as lungs or gills. However, there are some animals that respire without having a specific respiratory organ. One such animal is the earthworm.

Earthworms belong to the phylum Annelida and have a simple respiratory system. They do not possess lungs or gills like fish or frogs. Instead, earthworms respire through their moist skin, a process known as cutaneous respiration.

Cutaneous respiration in earthworms:
1. Moist Skin: Earthworms have a thin, moist, and permeable skin that allows the exchange of gases (oxygen and carbon dioxide) with the environment.
2. Moisture Retention: The skin of an earthworm needs to be kept moist for efficient gas exchange. The mucus secreted by the earthworm's skin helps in retaining moisture and prevents dehydration.
3. Capillary Network: The earthworm's skin is richly supplied with blood vessels arranged in a network called the capillary network. This network ensures a large surface area for gas exchange.
4. Diffusion: Oxygen from the environment diffuses through the earthworm's skin and enters the bloodstream, while carbon dioxide produced during cellular respiration diffuses out of the bloodstream and exits the body.

Advantages of cutaneous respiration in earthworms:
1. Efficient Gas Exchange: Earthworms have a large surface area for gas exchange, allowing them to efficiently obtain oxygen and eliminate carbon dioxide.
2. Adaptation to Environment: Earthworms live in moist habitats like soil or freshwater. The presence of a moist environment ensures the skin remains moist, facilitating gas exchange.
3. No Energy Expenditure: Unlike animals with lungs or gills, earthworms do not need to actively pump air or water to respire. They rely on passive diffusion through their skin.

Conclusion:
Earthworms respire through their moist skin, utilizing cutaneous respiration. This process allows them to exchange gases with the environment, obtaining oxygen and releasing carbon dioxide. Despite not having a specific respiratory organ, earthworms have adapted to efficiently respire through their skin in their natural habitat.