Allantoin is the oxidation product of uric acid. It is the excretory product in the embryos of amniotes. It is excreted through the extraembryonic membrane allantois.
Hippuric acid is seen among the excretory products only when the benzoic acid is present in the diet. It reacts with glycine to form hippuric acid. It is present in traces in human urine.
Amino acids are excreted in certain invertebrates like Unio, Lymnaea and Asterias. These animals are called amionotelic.
Guanine is the excretory material in spiders.
Creatinine is a waste product produced by muscles from the breakdown of a compound called creatine. Creatinine is removed from the body by the kidneys, which filter almost all of it from the blood and release it into the urine.