Most have no excretory structures, but rely on the diffusion of ammonia across their tissues to rid themselves of nitrogenous waste, though some have a simple excretory system.
All vertebrates share similarities in body structure; they all have a skeleton, a nervous system, a circulatory system, a digestive system and excretory system.
This set of structures is referred to as a "glomerulus" and may have an excretory function, since acorn worms otherwise have no defined excretory system.
As a result, the effects of diuretic peptides are often tested only on the tubules and their role in other parts of the insect excretory system is not investigated.