Systems of the Starfish
The Systems of the starfish are straightforward and easy to understand. The Water Vascular System (WVS) is important in the starfish as it controls the circulatory system and the starfishs movement. Water is drawn into the animal through a small opening in the central disc and is passed to canals running along each "arm". Along each canal are hollow, muscular tube feet that are found on the underside of the starfish, which are used to help the starfish move. Water is forced into the tube feet and they lengthen (like a sucker) then when the tube feet relax, water pushes back up through the canals and the tube feet shorten, releasing the suction and enabling the starfish to move. The starfishs gills are used to exchange gases, i.e. are the main organ of the respiratory system. The skin plays a lead role in the excretory system allowing diffusion of waste. The starfish reproduces by releasing sperm and ova through pores on the central discs, fertilization is external. The sperm and ova connect through hormones called pheromones, which are chemicals that guide behaviour. The young starfish develop in water. The WVS plays an essential role in the movement of the starfish while the exoskeleton of calcium carbonate protects the starfishs organs and delicate insides. The nervous system of the starfish is controlled by the nerve net on the central disc; nerve cords run along the arms and are connected to the eyespots. The digestive process is quite straightforward and is easily understood in relation to vertebrates. Food travels to the stomach, the digestive gland, undergoes chemical digestion and absorption digestion, goes through the WVS and then passes out of the starfish through the anus.
This is the starfishs phylum. Characteristics of this phylum include: a) spiny skinned organisms, b) radial symmetry, c) water vascular system, d) tube feet present and e) exclusively marine organisms. Other commonly known members of the Echinodermata family are sea cucumbers, sand dollars and sea lilies.
Starfish follow the following classification: