Unlike the organisms of the Archaea or Monera Kingdoms, the Animal Kingdom consists of multi-cellular, heterotrophic organisms that feed on other organisms to survive. Some of the characteristics of the animals in this kingdom are being able to develop throughout their lives, move independently and reproducing.
When studying classification, one of the most popular kingdoms to study is the animal kingdom because of course that's your own and so it's one you're most familiar with, at least you think so but when we take a closer look at some of the organisms in there, you're going to go, "That was an animal?" "Yes it is." So what are animals? Animal kingdoms are things that are animals are members of the kingdom that are multicellular and our cells have centrioles that we use during cell division but we don't have cell walls or chroloplasts like the plants and algae do. We are heterotrophs, what does that mean? Well hetero is a root word that means other and troph means nutrition, so we get our nutrition from other sources we don't make our own food. That's what plants are for, we hunt them down and kill them or we hunt down and kill the things that ate the plants like cows and rabbits and chickens and things. Now we are different from a lot of the other kingdoms and that we have nerves and muscles so that we can respond extremely quickly. If you walk up to a tree and you poke it, it's not going to respond. You poke it again, it's not going to respond. Now if you sat there, for years and years and kept poking, it'll start developing thicker bark and other things like that but it's going to be bored and just not do much in response to what you're doing and on the other hand if you walk up to a tiger and poke it, it will quickly respond and you will discover this is called high irritability. Now another thing that separates us from some of the organisms that are considered parts of the protozoa are that we're diploid and we have what's called the gametic life cycle that means that our entire life we're diploid except for our gametes which are haploid which means they only have only one copy of every chromosome. Now, let me take a quick look at this phylogenetic tree and show you some of the diversity that's within the animal kingdom. Now the animal kingdom ultimately derive from the protozoa, a member of the protist kingdom or protist group. Now branched off very quickly from them are the sponges, the porifera and many people consider them not really a member of the true animal or true metazoa kingdom. The Cnidaria another major group, one of the most primitive animal groups out there. They're the jellyfish, they have stinging cells and they just sit there and just float around like you've seen in Finding Nemo or there's the sea anemone form that's more sessile that means it doesn't move around much and that's what Nemo's dad lived in. Then we branch off, this branch over here leads to the echinodermata which is a big name for the star fish that you're familiar with as well as the chordata and that's things like us and frogs and birds and fish that have a backbone nerve called that runs up our back. This branch over here includes things like the platyhelminthes a really big name for a really small creature. It's the flatworms, things like tapeworms or plenaria, those are platyhelminthes then there's the rotifers which are these weird little things with rotating mouth parts and the nematodes which are round worms that you can find in the soil or occasionally inside of other animals as parasites. Mollusks, are a broad group that includes things like clams, snails and octopi. Up here are the annelids, those are the earthworms, the segmented worms and then there's the arthropods, the jointed leg things. Those include bugs and spiders and shrimp and crustaceans like crabs so that gives you an idea the diversity of things that are within the animal kingdom.