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Phylum EchinodermataBiology 11
Spiny Radial symmetry Water vascular system Endoskeleton
General characteristics
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.
Endoskeleton
Enables sessile & slow‐moving animals to sense potential food, predators, and other aspects of their environment from all directions
Radial Symmetry
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
Echinoderm Diversity
Sea Stars (Class Asteroidea)
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 StarGeneral Characteristics
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 StarMovement and Support
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 StarWater Vascular System (WVS)
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 StarDigestion
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 StarCirculation of Nutrients
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 StarExcretion
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 StarNervous System
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
Sea StarReproduction
Sea Stars
Phylum Echinodermata Includes…
Brittle Stars Fragile: rays will
break off when picked up.
Phylum Echinodermata Includes…
Sea Urchinsand 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
Phylum Echinodermata Includes…