Arthropoda

There are many animals in the phylum anthropoda, some of which are crabs, spiders, caterpillars, butterflies, scorpions, and bees; basically insects, spiders and crustaceans (animals that have a hard outer shell and no bones inside them also known as an exo-skeleton.) Two examples of these animals are crabs and beetles. Arthropods have a segmented body with appendages (arms or legs) on each segment. Arthropods have bilateral symmetry, which means that they can be divided one way into two halves that look the same. Like the trapezoid and the scorpion shown below. Arthropods have two body openings, one at their head, one at the other end of their body at the end of the abdomen. Arthropods have a much simpler nervous system than humans, basically they have two nerves that go along the body, and have nerves branching off. The two main nerves fuse in the head to form a brain. Arthropods reproduce with eggs that the female lays and the males fertilize. Arthropods do not have a true circulatory system. They do not have viens or arteries, instead they have an copper based, oxygen carrying protein in their "blood", as opposed to humans who have iorn based hemoglobin to transpoer oxygen. Their "Blood" in pumped by many hearts, into the body cavity where it oxygenates the tissues.
Arthropods breathe in many different ways. Arthropods that live mainly in water have gills specialized for gas exchange in water. Arthropods that are terrestrial, or live on land, have internal surfaces to process oxygen, such as lungs. Some arthropods have an oxygen-absorbing membrane to help them obtain oxygen. Arthropoda is the largest phylum of animals in the animal kingdom.