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Aquatic animals (especially freshwater animals) are often of special concern to conservationists because of the fragility of their environments. Aquatic animals are subject to pressure from overfishing/hunting, destructive fishing, water pollution, acidification, climate change and competition from invasive species.
These animals are called "secondarily aquatic" because although their ancestors lived on land for hundreds of millions of years, they all originally descended from aquatic animals (see Evolution of tetrapods). These ancestral tetrapods had never left the water, and were thus primarily aquatic, like modern fishes.
The traits enabled animals to check area on land for safe spots if being chased by a predator in water, as well as being useful for searching for prey items above the water. The water-based lateral line system was used substantially by these aquatic tetrapods to detect danger from predators. [2]
Research by Jennifer A. Clack and her colleagues showed that the very earliest tetrapods, animals similar to Acanthostega, were wholly aquatic and quite unsuited to life on land. This is in contrast to the earlier view that fish had first invaded the land — either in search of prey (like modern mudskippers ) or to find water when the pond ...
Mammals evolved on land, so all aquatic and semiaquatic mammals have brought many terrestrial adaptations into the waters. They do not breathe underwater as fish do, so their respiratory systems had to protect the body from the surrounding water; valvular nostrils and an intranarial larynx exclude water while breathing and swallowing.
Airbreathing catfish : Amphibious species of this family may venture onto land in wet weather, such as the eel catfish (Channallabes apus), which lives in swamps in Africa, and is known to hunt beetles on land. [8] Labyrinth fish (Anabantoidei). This suborder of fish also use a labyrinth organ to breathe air.
In biology, being semi-aquatic refers to various macro organisms that live regularly in both aquatic and terrestrial environments. When referring to animals , the term describes those that actively spend part of their daily time in water (in which case they can also be called amphibious ), or land animals that have spent at least one life ...
Invertebrate is a blanket term that includes all animals apart from the vertebrate members of the chordate phylum. Invertebrates lack a vertebral column, and some have evolved a shell or a hard exoskeleton. As on land and in the air, marine invertebrates have a large variety of body plans, and have been categorised into over 30 phyla. They make ...