Lesson 2 of 13 · 6 min
Excretory structures in animals
NCERT §16 (opening text)
An earthworm in Meher's school garden has no kidneys at all, yet it too must clear wastes and keep its water and salts in balance. What does it use?
The lesson in notes
In short
Across the animal kingdom excretory organs vary: most invertebrates have simple tubular structures, while vertebrates have complex tubular organs, the kidneys.
Protonephridia (flame cells) are found in Platyhelminthes such as Planaria, in rotifers, in some annelids and in the cephalochordate Amphioxus. Their main job is osmoregulation: regulating ions and fluid volume.
Nephridia are the tubular excretory organs of earthworms and other annelids. They remove nitrogenous wastes and keep the fluid and ionic balance.
Malpighian tubules serve most insects, including cockroaches. They remove nitrogenous wastes and carry out osmoregulation.
Antennal glands, also called green glands, do the excretory work in crustaceans such as prawns.
Whatever the organ, excretion is more than dumping nitrogen: these structures also help keep the ionic and acid–base balance of the body fluids.