Animals are classified based on their structural features. Structural features are the physical features of an animal. Therefore, the animals that have the same or similar physical features are commonly in the same classification.
Vertebrates
Animals that develop a backbone as they grow are classified as vertebrates. The classification 'vertebrates' is further divided into 5 major classes: amphibians, birds, reptiles, mammals and fish.
Invertebrates Animals that do not have backbones are invertebrates. In the world most animals are invertebrates. The main phyla in this classification are cnidarians, arthropods, molluscs and worms.
- Cnidarians There are about 10,000 species of cnidarians. All cnidarians have stinging cells with a bag-like body that only has one opening surrounded by tentacles. Food goes into this opening and waste comes out. Cnidarians with bodies that stick to something like a rock are called polyps. Free-swimming cnidarians are called medusas. cnidarians mostly live in saltwater but some can be found in freshwater. Examples of cnidarians are jellyfish, corals and anemones.
- Amphibians Amphibians are classified as an vertebrate that has two stages in its life, most amphibians live early life underwater and the rest of their life on land. One example is a frog. They start their life as a tadpole and they a grow into a frog with lungs. Amphibians have a thin skin that needs to be kept damp or else it will dry out. Amphibians get heat from their surroundings, making them ectotherms. An ectotherm is an organism of which there is a small amount of internal heat in other words cold-blooded.
- Molluscs Most molluscs live in the water but some live on land. They have soft bodies that are sometimes covered with a shell. They have a large muscular 'foot' to help with movement, well-developed internal organs and a mantle that can secrete a shell. Molluscs include snails, octopuses, slugs and squids and are the second-largest phylum of animals.
- Reptiles Reptiles have dry scales and lungs and lay soft, leathery, waterproof eggs. They can live entirely on land and they include snakes, lizards, turtles and crocodiles. Dinosaurs were reptiles too. Reptiles are also ectotherms They lie in the heat to raise their body temperature but unlike humans the heat is only temporary. Therefore, they are not very active in cold weather. Reptiles do not have gills and can only breathe air. Also, most reptiles are carnivorous.
Worms There are three different phyla of worms, these are roundworms, flatworms and segmented worms. - Roundworms are sometimes parasitic. Parasitic means that they live off other animals. Other roundworms live in water or damp soil. They have long, unsegmented cylindrical bodies and a digestive tube. Some examples of roundworms include hookworms and intestinal roundworms. - Flatworms can also be parasitic or free-living but have have flat bodies unlike roundworms. There are about 20,000 species of flatworm. Examples are flukes and tapeworms. - Segmented worms are found on both and water. They have well-developed systems and segmented bodies. Leeches and earthworms are examples of segmented worms.
- Mammals Mammals are all endotherms, feed their babies with milk and have hair unless you shave them. Their hair is not all the same. Some types are wool and fur. Mammal's milk is formed in the mammary glands. These are known as breasts. Their hair and their mammary glands are the main features that define a mammal. In further detail, mammals can be split into three groups. The first is placental mammals that give birth to well-developed young. Some examples are cows, bats, humans and whales. Another is marsupials that give birth to tiny young that continues to grow in pouches. Examples are wombats, possums and kangaroos. The last type of mammal are monotremes. They, unlike the others lay eggs but their young still develop in a pouch. There are only 3 species of monotreme: the short-beaked echidna, the long-beaked echidna and the platypus.
Arthropods Arthropods are the largest animal phylum. 75% of all known animals are in this phylum. Arthropods can be found everywhere, on land, in the air and in water. They have segmented bodies, paired jointed legs and an external skeleton. Within arthropods the major classes are: insects, centipedes, millipedes, arachnids and crustaceans. - There are a million species of insects which is more than any other living thing. Insects have one pair of antennae and have three sections in their body which are the head, thorax and abdomen. - Centipedes live on land and also have one long pair of antennae. Their whole body is in segments and they have one pair of legs on each one. - Millipedes also live on land but have one short pair of antennae. Like the centipedes body, their bodies are segmented but more round. They have two pairs of legs on most segments. - Arachnids live on land but some live in the water. They have no antennae and only a few body segments. Arachnids have four pairs of legs and no jaws. Arachnids include: scorpions, mites, ticks and spiders. - Crustaceans live mostly in the water. They have two pairs of antennae and breathe through gills. Examples are: crabs, prawns and lobsters.
- Fish All fish have gills and scales, and most lay eggs. Fish can be divided into 3 major classifications. There are jawless fishes, bony fishes and cartilaginous fishes. Bony fishes have a skeleton of bone most fishes are bony fishes. Cartilaginous fishes have a rubber like cartilage making up their skeleton and paired fins. Cartilage is the same material that makes up the tip of our noses. Sharks and stingrays are in this classification. Jawless fishes are like cartilaginous fishes but they do not have paired fins. There are only about 45 species of jawless fishes.
- Birds All birds have feathers, even the ones who aren't able to fly and on their legs and feet they have some scales. They lay hard shelled eggs and breathe using their lungs.Unlike reptiles and amphibians, birds are endotherms. Endotherms make their own heat by using energy from their food to stay warm, in other words they are warm-blooded.