Final answer:
Organisms such as earthworms, amphibians, jellyfish, and flatworms exchange gases through their skin, which involves a network of capillaries and requires a moist surface for efficient diffusion. Insects have a tracheal system, whereas lungless salamanders breathe exclusively through their skin.
Step-by-step explanation:
There are several types of organisms that exchange gases directly through their skin, a phenomenon seen in earthworms, amphibians, and some marine animals such as jellyfish. For example, earthworms and amphibians have a moist skin with a dense network of capillaries beneath it that allows direct gas exchange with their environment. Additionally, organisms like jellyfish and flatworms perform gas exchange across their body surface due to their simple body organization and close proximity of all cells to the external environment. Flatworms have a flat body which increases the surface area for gas exchange with the surroundings.
More complex terrestrial organisms like insects utilize specialized structures for gas exchange. For instance, insects have a tracheal system, and land crabs may possess adaptations like book lungs or specialized areas for absorbing oxygen. Certain amphibians, such as lungless salamanders, rely on their skin exclusively to 'breathe' as they lack lungs and gills.
This process is crucial for these animals to not only exchange gases but also to facilitate osmoregulation, maintaining water and salt balance in their bodies. The skin needs to remain moist to allow gases like oxygen and carbon dioxide to dissolve and diffuse across the cell membranes for effective respiration.