Final answer:
Crayfish benefit from having gills attached to their walking legs as it aids in respiration by allowing efficient gas exchange with water, especially during locomotion. This adaptation ensures that crayfish can breathe effectively even in varying oxygen conditions found in their aquatic habitats.
Step-by-step explanation:
Having gills attached to walking legs would benefit crayfish in breathing by allowing direct contact of the gills with water, which is necessary for efficient gas exchange. Similar to land creatures that evolved to breathe air through special respiratory structures, crayfish, being aquatic arthropods, primarily rely on gills to obtain oxygen from the water. The movement generated by walking would facilitate water flow across the gills, enhancing the crayfish's ability to absorb oxygen. This adaptation allows crayfish, which often inhabit shallow waters where oxygen levels can vary significantly, to maintain gas exchange effectively even when they are not swimming.
In summary, both terrestrial and aquatic arthropods have adapted structures suited to their environmental conditions. Terrestrial arthropods have developed tracheal systems or book lungs for breathing air, while aquatic arthropods, like crayfish, use gills for extracting oxygen from water. Evolution has equipped these different groups of arthropods with appropriate respiratory systems ranging from tracheae and book lungs for land arthropods to filamentous gills for aquatic arthropods, ensuring survival in their various habitats.