Phylum Echinodermata Biology 11
General characteristics Spiny Radial symmetry Water vascular system Endoskeleton
Endoskeleton Hard, spiny, or bumpy endoskeleton covered with a thin epidermis. Endoskeleton composed of calcium carbonate (limestone). Some spines are modified into pedicellariae for protection or self cleaning. Can be either rigid (as when we try to pull one off of a rock) or very flexible (when righting itself), since endoskeleton is made of plates joined by muscles which can contract or relax.
Radial Symmetry Enables sessile & slow moving animals to sense potential food, predators, and other aspects of their environment from all directions
Echinoderm Diversity 1. Class Asteroidea: Ex. Sea stars Most species have 5 or more arms 2. Class Ophiuroidea: Ex. Brittle Star & basket star Compact size; move quickly Arms used for motility
Echinoderm Diversity 3. Class Crinoidea: Ex. Sea lilies & feather star Few living species remain Sea lilies are attached to the ocean floor Feather stars begin attached but break away and swim freely 4. Class Echinoidea: Ex. Sea urchin & sand dollar Bodies shaped like spheres or disks; no arms Solid, internal shell Special feeding structures called Aristotle s lantern: made up of five sharp, triangular tooth likes structures surrounding the mouth
Echinoderm Diversity 5. Class Holothuroidea: Ex. Sea cucumber No arms; elongated body Bilaterally segmented Lie and move on one side only
Sea Stars (Class Asteroidea)
Sea Star General Characteristics Radial symmetry Have a dorsal and ventral side, but no anterior and posterior ends Five part body plan NO cephalization (i.e. no brain)
Sea Star Movement and Support Movement carried out by WATER VASCULAR SYSTEM WVS: A network of fluid filled tubes that enable the sea star to move Along the underside of each of the sea star s arms are many pairs of TUBE FEET Tube feet: external structures of the water vascular system On top of each tube foot is an AMPULLA Ampulla: muscular sac that helps force water through the WVS Muscles of the ampullae contract, pushing water into the tube foot causing it to extend When the foot attaches to a surface, it contracts, pushing the water back into the ampullae and pulling the sea star forward
Sea Star Water Vascular System (WVS) System enables them to move, exchange gases, capture food, and excrete wastes Water enters the madreporite ring canal long radial canals hollow tube foot
Sea Star Digestion All echinoderms have a mouth, stomach and intestines. Sea stars are carnivorous Feed on mollusks by extruding their stomach through their mouth onto the food. Tube feet aid in prying apart shells of mollusks. Powerful enzymes are secreted by a pair of digestive glands in each arm The stomach then absorbs the liquid food. (No intestine needed).
Sea Star Circulation of Nutrients There is a heart like sac under the madreporite that pushes fluid nearly identical to seawater through the coelem, bathing all organs The fluid is kept in motion by beating cilia. Skin gills and tube feet bring in oxygen to this fluid.
Sea Star Excretion Wastes are flushed from body through the tube feet or skin gills. A sea star also has an anus, located in the center of the dorsal side.
Sea Star Nervous System No brain or even fused ganglia, only a central nerve ring that surrounds the mouth Nerves extend from the nerve ring down each ray (below radial canals) into a nerve net that is sensory and coordinates movement No sensory organs, only cells that detect light & touch Have eyespots at the end of each arm that allow them to detect light, and chemical receptors on their tube feet
Sea Star Reproduction Sea stars are separately sexed. Two ovaries or testes lie in the corners of each arm and open directly to the exterior Spawning by one can result in those nearby to also spawn
Phylum Echinodermata Includes Sea Stars
Phylum Echinodermata Includes Brittle Stars Fragile: rays will break off when picked up.
Phylum Echinodermata Includes Sea Urchins and Sand Dollars Covered in spines. No rays
Phylum Echinodermata Includes Sea Cucumbers Leathery covering allows flexibility. When threatened, may expel tubes from anus or release internal organs to confuse predator.
Phylum Echinodermata Includes Sea lilies and Feather stars Feathery arms allow it to swim.
Phylum Echinodermata Includes Sea daisies Tube feet located around edge of disk. Less than 1 cm in diameter Discovered in 1986