Write a short note on ammonotelism.

Hint: The process of excretion of a toxic waste product which is mostly produced in the case of aquatic organisms.

Complete step-by-step answer:
Excretion is the removal of metabolic waste from the body to maintain the solute balance.
The excretion of ammonia and ammonium ions in an organism is known as ammonotelism. Those organisms which excrete by the process of ammonotelism are known as ammonotelic organisms. In this process organisms usually produce ammonia as a waste product. Ammonia is highly toxic and must be removed from the body as early as possible. It needs a high quantity of water to get dissolved and then removed through excretion.
Ammonia is highly soluble in water, thus all ammonotelic organisms are aquatic animals. Animals including protozoans, crustaceans, cnidarians, Platyhelminthes, poriferans, echinoderms, and other aquatic invertebrates are ammonotelic organisms.
Metabolic waste or excrements are substances leftover from the metabolic processes which cannot be used by the organism and must be excreted. The metabolic waste includes nitrogen compounds, water, carbon dioxide, phosphates, sulfates, etc., which are treated as excretes by animals. All the metabolic wastes are excreted in a form of water solutes through the excretory organs like nephridia, malpighian tubules, kidneys, etc. The carbon dioxide is not excreted through excretory organs instead it is excreted together with the water vapor throughout the lungs.
The ornithine cycle, also known as the urea cycle which converts the highly toxic ammonia to urea for the excretion. It occurs mostly in uricotelic organisms. Most aquatic organisms, or ammonotelic animals, excrete ammonia without converting it into urea. This occurs because of the amino acid catabolism which results in the formation of ammonia as a waste product.

Note: Three types of substances are excreted by an organism: ammonotelism (excretion of ammonia and ammonium ions), ureotelism (excretion of urea), and uricotelism (excretion of nitrogen in the form of uric acid).