1. Exoskeleton-<span>Arthropods are invertebrates, which means their bodies do not have internal bones for support. To compensate for this, they produce a hard exoskeleton made of chitin, a mixture of lipids, carbohydrates and protein, which covers and protects their bodies like a suit of armor. As arthropods grow, they must shed or molt their exoskeletons. They first produce new, softer exoskeletons underneath the old ones. Once their hardened, old coverings crack and shed, they sport roomier, albeit soft, exoskeletons. Arthropods are incredibly vulnerable during the molting process, and will often hide until their new exoskeletons harden.</span> 2. Segmented bodies-Arthropods have bodies that are internally and externally segmented. The number of segments depends on the individual species; millipedes, for example, have more segments than lobsters. 3. Jointed Appendeges-The name arthropod actually comes from the Greek “arthro,” meaning joint, and “pod,” meaning foot. All arthropods have jointed limbs attached to their hard exoskeletons that allow for flexibility and movement. The joints generally bend in only one direction but allow for sufficient predatory and defensive actions. 4. Bilateral Symmetry-An arthropod's body can be divided vertically into two mirror images. This is called bilateral symmetry. An arthropod shares this symmetry with many other animals such as fish, mice and even humans. Other animals such as the jellyfish and sea star exhibit radial symmetry, while coral and sea sponge are asymmetrical -- exhibiting no pattern at all. 5. Open Circulation System-An arthropod has an open circulatory system. This means instead of a closed circulatory system of interconnected veins and capillaries, an arthropod’s blood is pumped through open spaces called sinuses in order to reach tissues. An arthropod does, however, have a heart which pumps blood into the hemocoel, the cavity where the organs are located, where it surrounds the organs and tissues.
The cells inside our bodies are “specialized.” This means that each type of cell performs a unique and special function. For this reason, each of the 200 different types of cells in the body has a different structure, size, shape, and function, and contains different organelles.
We are multicellular organisms, different types of cells are required to do different function.
