Aquatic vs Terrestrial Animals
The fundamental difference between aquatic and terrestrial animals is their habitat and their adaptation to that habitat. Almost all the habitats found in the world can be put into two major habitats; aquatic and terrestrial. Aquatic ecosystems are found in water bodies and can be categorized into two broad groups; marine ecosystem (oceans and seas) and freshwater ecosystem (rivers, lakes, etc). Terrestrial ecosystems are the habitats found on lands like forests, wetlands, deserts, grasslands, etc. Animals including vertebrates and invertebrates have developed various adaptations that enable them to live in either of these habitats. Most animals are entirely spending their lifetime in aquatic or terrestrial environments. However, some animals are adapted to live in both terrestrial and aquatic environments, thus called semi-aquatic animals (ex: amphibians, platypus, crocodiles, etc.).
What are Aquatic Animals?
Animals who live in water for entire life time or most of their lifetime are called aquatic animals. Both aquatic invertebrates and vertebrates developed entirely different adaptions to live in water unlike the animals that live on land. Aquatic animals can be divided into two broad groups depending their aquatic habitat, namely; marine animals and freshwater animals. Some examples for aquatic invertebrates include jellyfish, corals, sea anemones, hydras, etc. These invertebrates are adapted to acquire dissolved oxygen directly from water. Aquatic vertebrates include bony fishes, cartilaginous fishes, whales, turtles, dolphins, sea lions, etc. Except fishes, all the other vertebrates need to take air from the atmosphere as they are unable to extract dissolved oxygen from the water. Unlike the land animals, aquatic animals like fish, aquatic mammals have fins and streamline bodies that enable them to move fast in the water.
What are Terrestrial Animals?
Terrestrial animals are the animals who live on land for most or all of their life span. Fossil records proved that a group of sea creatures, related to arthropods was the first animals to invade the land around 530 million years ago. The other early aquatic animal groups who invade lands include primitive vertebrates, arthropods and mollusks. Scientists believed that these primitive animals are the early ancestors of modern terrestrial animals. Some animals like roundworms, tardigrades and rotifers are not considered as truly terrestrial animals because they still need water to live. In the Kingdom Animalia, all known species of Arthropods, gastropods, and chordates are true terrestrial animals with adaptations to live in dry terrestrial habitats. Moreover, the species of these three groups lack aquatic phase in their life cycles.
What is the difference between Aquatic and Terrestrial Animals?
• Aquatic animals are the animals that live entirely or most of their lifetime in the water. Terrestrial animals are the animals who live entirely or most of their lifetime on lands.
• Examples for aquatic animals include hydra, jellyfish, corals, sea anemones, whales, dolphins, and fishes, while examples for terrestrial animals include species of arthropods, gastropods, and chordates.
• Unlike the terrestrial animals, aquatic animals have adaptations like streamline bodies, webbed feet, fins, air bladder, etc.
• Some aquatic animals can utilize dissolved oxygen in the water, but terrestrial animals cannot.