Final answer:
Desert mammals have the longest loops of Henle in their kidneys, an adaptation for water conservation in arid environments.
Step-by-step explanation:
The animals with the longest loops of Henle in their kidneys are desert mammals (option e). The loop of Henle is a crucial part of the mammalian renal tubule that allows these animals to produce highly concentrated urine.
This adaptation is especially important for water conservation in arid environments where water is scarce. Desert mammals have evolved juxtamedullary nephrons with longer loops of Henle, enabling them to reabsorb more water and thus regulate urine concentration effectively.
Aquatic animals typically do not need such an adaptation since water is readily available in their environment. Additionally, mammals have specific features like a urinary bladder and lack a renal portal system, further distinguishing their excretory systems from those of other vertebrates.