Final answer:
Desert mammals spread lipids on their skin to reduce EWL and often store water in their urinary bladders as an adaptation to arid environments.
Step-by-step explanation:
Animals that spread lipids on their skin to reduce evaporative water loss (EWL) and store water in their urinary bladders are generally desert mammals. This adaptation is important for survival in arid environments where water is scarce. On the contrary, aquatic mammals, like otters, spread hydrophobic lipids in their fur to protect them from the elements, but do not face the same challenges of EWL that desert mammals do. Amphibians typically have permeable skin that requires a moist environment to function properly, and while reptiles have adapted to terrestrial life with scales containing keratin and waxy lipids to prevent EWL, they do not typically store water in their urinary bladders. Instead, reptiles excrete uric acid to conserve water. Desert mammals, however, exhibit both behaviors as a means of adapting to a dry environment where conserving water is critical for survival.