Animal Facts
By Laura Klappenbach, About.com Guide to Animals / Wildlife
Scientists estimate that there may be between 3 and 30 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.
- Insects - Insecta
- Mammals - Therapsida
- Molluscs - Mollusca
- Ray-Finned Fishes - Actinopterygii
- Reptiles - Reptilia
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. All animals have cells that lack rigid cell walls (like those found in plant cells).
- Animals (Metazoa)
- Chordates (Chordata)
- The Six Basic Groups of Animals
- What Makes an Organism an Animal?
- How Many Animal Species Are There?
- An Introduction to Zoology
- The Basics of Vertebrate Evolution
- Guide to Vertebrates / Invertebrates
- Comparing Prokaryotes and Eukaryotes
- Quiz: Know Your Animal Groups
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. Amphibians first appeared during the Devonian Period, 370 million years ago.
Arthropods - Arthropoda
Arthropods (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. Arthropods are a highly successful group of animals—they account for over three quarters of all currently known living and fossil organisms.
- Lobster's Unique Sounds Defy Predators
- African Spider Preys on Mosquitos
- The Tangled Web of Spider Classification
Birds - Aves
Birds (Aves) are unique creatures having wings, feathers, hollow bones, and other adaptations for an aerial lifestyle. Flight consumes a great deal of energy and consequently these warm-blooded animals have high metabolic rates. Birds evolved from reptiles during the Mesazoic Era about 150 million years ago. Today, an estimated 9000 species of birds inhabit our planet.
Cnidarians - Cnidaria
Cnidarians (Cnidaria) are animals characterized by radial or biradial symmetry. Members of the Phylum Cnidaria includes jellyfish, hydra, sea anemones, corals, and sea pens. The basic body form of these animals is simple, consisting of a stomach sac with one opening. Cnidarians have life cycles that progress througw two body forms, a free-swimming medusa and a sessile polyp.
Insects - Insecta
Insects (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. The body of an insect is made up of a head, thorax, abdomen, a pair of compound eyes, a pair of antennae, and a set of complex mouthparts.
- Insects (Insecta)
- The Cicadas are Coming
- New Order of Insects Identified
- A Pond Full of Backswimmers
- 17-Year Cicadas: From Nymph to Adult
Mammals - Therapsida
Mammals (Therapsida) 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. Mammals have successfully adapted to and colonized a wide variety of habitats including land, air, and water. Their widespread success is largely due to their ability to regulate their own body temperature.
Molluscs - Mollusca
Molluscs (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 other groups of organisms. There are an estimated total of more than 250,000 species of molluscs. The branch of zoology known as 'malacology' is the study of molluscs.
- Mollusks (Mollusca)
- Gastropods, Slugs and Snails (Gastropoda)
- A Natural History of Terrestrial Snails
- California Sea Hare (Aplysia californica)
- Ten Facts About Octopi
Ray-Finned Fishes - Actinopterygii
Ray-Finned Fishes (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. During the Late Triassic a group of ray-finned fishes called 'teleosts' first appeared.
- Firefish (Pterois volitans)
- Cichlids - Family Cichldae
- Ray-Finned Fishes (Actinopterygii)
- Ten Facts About Fishes
Reptiles - Reptilia
Reptiles (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 amniotic eggs. Reptiles gave rise to the birds and the mammals.
