Question

How do different species maintain water balance in saltwater systems?

Answer 1

Osmoregulation and maintenance of salt-water balance is highly critical for survival of species. Different evolutionary species from small animals to complex animals utilize different strategies for osmoregulation. Some of these strategies are discussed as below:

1. Sponges and cnidariana: These simple organisms do not possess any specific cellular system or organ to eliminate salt and liquid waste from the body. Instead, they simple reside in water and diffuse the salt contaning water out of the body.
2. Small single cellular organisms like Paramecium have an excretory vacuole present inside their cytosol which helps them to collect, store and eliminate the excessive salts and waste from their body.
3. Platyhelminthes have developed special "flame cells" which represent organ of liquid waste excretion from their body.
4. Advanced organisms such as annelids, molluscs (some members only) etc contain a primitive form of meta-nephridia or ruminent filtration cell system which filters the salts and water present inside their body.
5. The echinoderms have a more advanced system of filteration of water and salts called the filtration canal present synchronous to the radial symmetry of the body which helps to filter the required cells and food from water and expells out undesirable salts and liquid waste outside.
6. Higher organisms such as fishes have developed a more advanced renal system with very long loop of Henle which ensures elongated and efficieny reasbsoprtion of salt-free water to maintain osmoregulation in their body.
7. More advanced organisms such as amphibians have evolved with renal systems with shorter loop of Henle which ensures large re-absorption of water from the filtrate and elimination of liquid waste comprising of excessive salts and urea.

Thus, this description implies that different types of aquatic species have derived different types of osmoregulatory cells/organs/organ systems to maintin water-salt balance depending upon their complexity and nature.