One of the most basic ways of categorizing animals is to break them down into animals with backbones and animals that do not have backbones. The animals that have backbones are called vertebrates. This word comes from the word that we use for the bones that make up the backbone. Those bones are called vertebrae so the animals are vertebrates. The animals that do not have backbones are called invertebrates.
Some examples of vertebrates include human beings, cats, dogs, fish, elephants, and chickens.
Some examples of invertebrates include spiders, worms, and flies.
Over 95% of the animals on Earth are invertebrates: animals without a backbone. The remainder of animals are vertebrates: animals with a backbone.
Invertebrates can be classified into many different groups, and each group of invertebrates can be further broken down into even more subgroups based on characteristics of the organism. The most common group of Invertebrates are Arthropods: animals with bilateral symmetry, exoskeletons, jointed legs, and 6 or more legs. Arthropods are divided into subgroups such as:
- insects (6 legs, antennae/wings, 2 compound eyes) - ants, butterflies, grasshoppers.
- arachnids (8 legs, no wings/antennae, up to 8 eyes) - spiders, scorpions, ticks, mites.
- crustaceans (10 or more legs), diplopods, and more. - crabs, lobster, shrimp.
Vertebrates are commonly grouped into 5 major groups:
- Birds (wings, feathers, 2 legs, beak, lay eggs) - penguins, ostriches, owls.
- Reptiles (scaly, rough skin, lay eggs) - lizards, alligators, snakes.
- Amphibians (smooth slimy skin, live on land and in water) - frogs, salamanders.
- Mammals (fur or hair, give live birth, mammary glands) - humans, whales, bats.
- Fish (scales, gills, fins, lay eggs) - tuna, bass, flounder.
Animals with a backbone (spinal columns) and a cranium base are classified as vertebrates. Animals that lack such a column are called invertebrates. There are more than 1 million known species (kinds) of invertebrates and about 40,000 species of vertebrates.
Most vertebrates have a spinal column made of bones called vertebrae. But some, such as the shark, do not have a bony spinal column. Sharks have vertebrae made of cartilage.
All vertebrates are bilaterally symmetrical - that is, the left and right sides of the body are alike. The body is usually divided into a head and a trunk. The more advanced land vertebrates have a neck. In mammals, the trunk is divided into a thorax (chest) and abdomen. Vertebrates never have more than two pairs of limbs.
Most vertebrates have a spinal column made of bones called vertebrae (see SPINE). But some, such as the shark, do not have a bony spinal column. Sharks have vertebrae made of cartilage.
Vertebrates are classified in the phylum chordata and make up the subphylum vertebrata. They may be further divided into eight classes: (1) hagfishes ; (2) lampreys; (3) sharks and other cartilaginous fish; (4) bony fish; (5) frogs and other amphibians; (6) reptiles; (7) birds; and (8) mammals.
As invertebrates include a very large number of animals which have been classified by scientissts in several major groups called phyla including porifera, cnidaria, cnidarians, platyhelminthes, nematoda, annelida, echinodermata, mollusca, and arthropoda.