Terrestrial animal

Terrestrial animals are animals that live predominantly or entirely on land (e.g., cats, chickens, ants, most spiders), as compared with aquatic animals (e.g., fish, whales, octopuses, lobsters, etc.), who live predominantly or entirely in bodies of water; and semiaquatic animals (e.g., crocodilians, seals, platypus and most amphibians), who inhabit coastal, riparian or wetland areas and rely on both aquatic and terrestrial habitats. While most insects (who constitute over half of all known species in the animal kingdom) are terrestrial, some groups, such as mosquitoes and dragonflies, spend their egg and larval stages in water but emerge as fully terrestrial adults (imagos) after completing metamorphosis.

Terrestrial animals conduct respiratory gas exchange directly with the atmosphere, typically via specialized respiratory organs known as lungs, or via cutaneous respiration across the skin. They have also evolved homeostatic features such as impermeable cuticles that can restrict fluid loss, temperature fluctuations and infection, and an excretory system that can filter out nitrogenous waste in the form of urea or uric acid, in contrast to the ammonia-based excretion of aquatic animals. Without the buoyancy of an aqueous environment to support their weight, they have evolved robust skeletons that can hold up their body shape, as well as powerful appendages known as legs or limbs to facilitate terrestrial locomotion, although some perform limbless locomotion using body surface projections such as scales and setae. Some terrestrial animals even have wings or membranes that act as airfoils to generate lift, allowing them to fly and/or glide as airborne animals.

In a narrower sense, the word "terrestrial" is used to specifically describe animals that live on the ground (particularly those living obligately on the soil surface), as opposed to arboreal animals that live in trees, even though trees, like the shrubs and groundcovers from the lower layers, are all an integral component of the terrestrial ecosystem.

Ecological subgroups

The term "terrestrial", in a more specific sense, is typically applied to species that live primarily on the ground or in burrows inside the soil, in contrast to arboreal species, who live primarily in trees, even though the latter are actually a specialized subgroup of the terrestrial fauna.

There are other less common terms that apply to specific subgroups of terrestrial animals:

Saxicolous organisms are rock-dwelling. "Saxicolous" is derived from the Latin word saxum, meaning a rock.