PHYLUM ECHINODERMATAMembers of this Phylum include starfish, brittle star, sea cucumbers, sea urchins, sand dollars, and sea lilies. As larva, they are bilaterally symmetric and as adults they are radially symmetric, being divided into five segments. All have a water vascular system for locomotion and feeding. All have tube feet, primarily for locomotion. All have an endoskeleton with spines protruding through its epidermis (skin). Their nervous system and sensory organs are poorly developed. There is no head. They are only marine animals. Echinoderms and chordates arose from a common ancestor.EXTERNAL ANATOMYPreserved specimens are rigid but this is not the case with living specimens.The body is covered with a thin ciliated epidermis, which itself overlays an endoskeleton. You will see white calcareous spines in the epidermis. See the demo for the following: on the surfaceof the epidermis and surrounding the spines are pedicellariae, used for defense and cleaning.The body consists of five arms or rays surrounding a central disk. There are two sides: an oral side which is the side the mouth is located and an aboral side, the side away from the mouth. Located on the aboral side is a small (1/8”) circular plate, the madreporite plate. This plate is porous and allows water to enter the water vascular system. The two rays on either side of the plate constitute the bivium; the other three rays are called the trivium.On the oral side there is a groove running down the center of each arm. This is the ambulacral groove. Within this groove are rows of tube feet, part of the water vascular system. The tube feet end in suction cups.INTERNAL ANATOMYREAD THE NEXT PARAGRAPH IN ITS ENTIRITY FIRST, AND THEN DO.Locate the middle arm of the trivium. Using scissors, cut ¾” off the tip of the ray. Next cut both sides of the ray so that when pulled apart there is an aboral top and an oral bottom; continue cutting on the aboral side along the outer edge of the central disk ending up on either side of the madreporite plate. REPEAT: ENDING UP ON EITHER SIDE OF THE PLATE. Now lift up the epidermis/endoskeleton covering the innards ofthe arm and the central disk. If necessary detach clinging organs by probe or further cutting.The organ that usually adheres to the underside of the lifted epidermis/endoskeleton is a large grained, somewhat feather shaped organ, the pyloric seca also called the digestive gland. It secretes enzymes used to digest absorbed nutrients. Underneath the pyloric seca, you may find finely grained structures, the gonads. They will be laying in the bottom half of the arm. Presence or size will depend on the sexual maturity of the starfish and whether or not the specimens were collected during the spawning season. The stomach fills the central disk area. The coelom is the cavity that everything fits in. The raised ridge of cartilage running down the middle of the exposed arm innards is the ambulacral ridge; it covers the radial canal which is part of the water vascular system.WATER VASCULAR SYSTEMThe water vascular system is found only in enchinoderms and is used for locomotion and prey capture. It consists of the madreporite plate, stone canal, ring canal, radial canal, and tube feet which may or may not contain suction cups.PROCEED CAREFULLY WITH STOMACH REMOVAL SO AS NOT TO DESTROY THE STONE CANAL.Take your blunt nosed tweezers and pull the stomach out of the central cavity. Note that the ring canal is embedded within the ring of cartilage and the radial canal is under the ambulacral ridge. Ampulla as pictured are inflated but in your specimen might appear as deflated sacs along the sides of the ambulacral ridge. Although ‘lateral canals’ are part ofthe water vascular system, you will not be able to see them. To see the tube feet and theirsuction cups, turn your starfish over to oral side and spread open an ambulacral