Question

What is meant by aquatic and terrestrial animals?

Answer 1

Animals are found in two domains of the ecosystem – in water and on land. These two domains form the habitat of animals in the ecosystem. Animals residing in these habitats differ in their body structures and functions.

Complete answer: Our ecosystem can be divided into two habitats – land and water. Animals and plants found in the ecosystem are adapted to reside in one of the two habitats.
Water supports both animal and plant life forms. Organisms that live in water are called Aquatic. The term aquatic refers to both salt and freshwater species.
Aquatic animals spend most of their lifetime in water. To bring about the basic life processes, the aquatic organisms have developed certain special structures.
For example, to breathe in water the animals have developed gills instead of lungs. The gills are capable of taking in dissolved oxygen. This is brought when water passes over the gills. Gills are richly supplied with blood vessels. When water is passed over the vessels, dissolved oxygen is absorbed and carbon dioxide is diffused out. The efficiency of the process is enhanced by a countercurrent mechanism, where the direction of water passage over the gills is opposite to that of blood flow. It helps recover most of the dissolved oxygen in water. In addition, certain aquatic animals like whales breathe in air.
The appendages of aquatic animals have evolved to form fins. This helps the animals to move swiftly in water. Other modifications include streamlined bodies and presence of swim bladders. Many invertebrates are also aquatic like shrimps, beetles, etc.
Animals living on land are called terrestrial animals. These animals spend their lifetime on land. There are millions of animals living on land including invertebrates and vertebrates. To live on the land these animals have modifications like presence of lungs for respiration and hands, feet for locomotion. Some terrestrial animals also exhibit limbless locomotion like snakes.
Examples of aquatic animals are fishes, shrimps, beetles, some snakes. Terrestrial animals are lions, tigers, snakes, spiders, bats, etc.

Note: Animals can be aquatic or terrestrial according to their habitats. The animals living in each of these domains have developed special structures to make their life easier. However, some animals can live in water as well as on land like frogs. These animals have adaptations like webbed feet, skin that inhibits loss of water, special ear drums to survive land and in water.