Animals

Marine Fish
Fish are magnificently diverse in size, shape, color, and pattern. Almost all have fins, gills, and scales. About 96 percent are bony fish. The rest are cartilaginous fish, like sharks, skates, and rays.

Freshwater Fish
An estimated 41 percent of fish species are found in fresh water with conditions that differ in many ways from marine environments, such as salinity. Freshwater fish have gills that diffuse water, while at the same time keep the salts of bodily fluids inside.

Invertebrates
No bones about it! Most of the world’s animal species—up to 99 percent—are invertebrates! These diverse creatures have one common characteristic: They lack the backbone and accompanying skeleton of vertebrates. Some invertebrates are very soft, but most have some support structure.

Amphibians
Frogs, toads, and salamanders are some familiar examples of amphibians. Amphibians are cold-blooded (ectothermic), smooth-skinned vertebrates (animals with backbones) that are capable of living both on land and in water, usually in different stages of their lives.

Reptiles
When people think of reptiles, most think of snakes, but reptiles also include chelonians (turtles and tortoises), crocodilians (crocodiles, alligators, caiman, and gavials), lizards, and tuataras. They are air-breathing vertebrates with tough, waterproof skin that retains moisture.

Invasive Species
Balance within an ecosystem is important, and a non-native animal may have an adverse reaction to or on its new habitat. Experts have also introduced non-native animals and plants to restore aquatic or ecological balance in habitats with much success.