Digestive system: Patrick eats by using his mouth which is also connected to the cardiac stomach. He has have a complete digestive system with a mouth at the center of their underside (the "oral" side) and an anus on their upper surface (the "aboral" side).
Circulatory system: Patrick's circulatory system includes the perivisceral coelom (basically, the space inside the body but outside the various organs), the water vascular system (of which the tube feet are the most obvious part), and the hemal system (which actually looks something like a circulatory system).
Nervous system: The central nervous system of a starfish consists of a radial nerve running the length of each ray and a circumoral ("around the mouth") nerve ring that connects the radial nerves. Contrary to what you might expect, the nerve ring doesn't seem equipped to do any kind of processing of information. Instead, all the sensory information must go to the radial nerves, any memories must be stored in the radial nerves, and any decisions about what to do must be made in the radial nerves. And somehow, the five different radial nerves must coordinate those decisions if the starfish is going to get anywhere.
Excretory system: Coelomic fluid, circulated by ciliary action, performs many of the normal functions of a circulatory system.
Reproductive system: A female starfish sheds in two hours several millions of eggs into the water, with a mean diameter of 0.16-0.19 mm . After fertilization, a hollow ball develops, called the blastula. The cells of the blastula possess cilia on the outside for swimming. After one day a deep groove develops, leading to the gastrula. The gastrula's of all types of echinoderms are very similar. But then differentiation starts. The common starfish develops a so-called bipinnaria larva, with ciliated bands running about the periphery. After several weeks the bipinnaria larva takes on a more elaborate form, with longerprojecting arms and after some more weeks, a brachiolaria larva is formed. The larvae have their own gut, with inside cilia to inhale and transport food particles. They feed themselves with diatoms and other organisms in the plankton. The stomach is large and round and situated at the backside. After this phase a large part of the larva degenerates and at the rear side a rudimentary formed juvenile starfish develops. The organs of the young starfish are formed anew.
Integumentary system: Tough skin protecting the vital organisms. Some species have spikes for additional protection.
Body plan: Radial symmetry, no head.
Patrick or other sea stars are found in most of temperate and tropical oceans of the world. They are exclusively marine and are bottom dwellers.
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