Animal Facts
Scientists estimate that there may be between 3 and 50 million species of animals on our planet. The exact number of species on Earth remains unknown, and new species are discovered all the time. Animals inhabit all corners of the globe, from the icy polar regions, to the depths of the ocean, to the tops of mountains. The profiles available at this site will help you become familiar with just a few of the many animal groups with whom we share our planet.
Featured Topics
- Animals - Metazoa
- Animals (Metazoa) are multicellular organisms that are capable of locomotion and rely on other organisms to obtain their nourishment. There are many different groups of animals, among which the better known groups are amphibians, birds, invertebrates, fishes, mammals, and reptiles.
- Amphibians - Lissamphibia
- Amphibians (Lissamphibia) include animals such as salamanders, newts, caecilians, frogs, and toads. These animals' ancestors were the first to venture out from the water and adapt to life on land. Amphibian larvea are often aquatic and go through a complex metamorphosis process as they grow to adulthood.
- Arthropods - Phylum Arthropoda
- Arthropods (Phylum Arthropoda) include insects, spiders, crustaceans, scorpions, and centipedes. Arthropods are bilaterally symmetrical and have segmented bodies. Their body is covered with an exoskeleton and many arthropods have compound eyes.
- Birds - Class Aves
- Birds (Class Aves) are unique creatures having wings, feathers, hollow bones, and other adaptations for an aerial lifestyle. Birds evolved from reptiles during the Mesazoic Era and today, an estimated 300 billion birds belonging to more than 9000 species inhabit virtually every terrestrial habitat on the planet.
- Cnidarians - Phylum Cnidaria
- Cnidarians (Phylum Cnidaria) are animals characterized by radial or biradial symmetry. Members of the Phylum Cnidaria includes jellyfish, hydra, sea anemones, corals, and sea pens. Cnidarians have life cycles that progress through two body forms, a free-swimming medusa and a sessile polyp.
- Insects - Class Insecta
- Insects (Class Insecta) are a highly successful group of animals. With somewhere between 750,000 and 30 million species of insects alive today, insects account for more species of animals than any other class of animals. Insects have small body sizes but are extremely variable in shape and form.
- Mammals - Class Mammalia
- Mammals (Class Mammalia) are characterized by mammary glands, hair, a diaphram, a four-chambered heart, and a large cereberal cortex. 70 million years ago when reptile diversity declined, mammals took over habitats once unavailable to them.
- Molluscs - Phylum Mollusca
- Molluscs (Phylum Mollusca) are a highly diverse group of animals that include cephalopods (squid, octopuses, cuttlefish), gastropods (nudibranchs, snails, slugs, limpets, sea hares), bivalves (mussels, clams, oysters, scallops) and many others. There are an estimated total of more than 250,000 species of molluscs.
- Ray-Finned Fishes - Class Actinopterygii
- Ray-Finned Fishes (Class Actinopterygii) are a diverse group of aquatic vertebrates—over half of all living vertebrate species (aquatic and terrestrial) belong to this class. The first bony fishes apeared during the Devonian Period and underwent significant expansion and diversification during the Carboniferous Period.
- Reptiles - Class Reptilia
- Reptiles (Class Reptilia) are cold-blooded vertebrates that evolved from amphibians about 340 million years ago. There are two characteristics that distinguished early reptiles from amphibians and enabled them to colonize terrestrial habitats more extensively than their ancestors, scales and the ability to lay hard-shelled eggs.
