Animals that excrete ammonia are referred to as ammonotelic - and all are aquatic. However, it s quite toxic and requires abundant water. This is a fairly soluble compound that is more expensive to synthesize than ammonia, but is less toxic. Animals that excrete urea are known as ureotelic. This is a very insoluble compound, but is also not very toxic at all.
Uric acid is basically a purine, and is the most expensive nitrogenous waste product to produce.
However, it requires the least amount of water to be excreted, so it is seen in terrestrial organisms that need to conserve water as much as possible. A. Contractile Vacuoles Used by Sponges B. Nephridial organs Common in many invertebrate animals These animals tend to show only filtration and reabsorption, not selective secretion. There are two types of Nephridia 1. This is a paired gland in the head region of the crustacean. These organs are capable of filtration, reabsorption, and secretion.