30.1    An overview of Echinoderms

	Echinoderm - marine vertebrate characterized by spiny skin, radial symmetry, a water vascular system, and an endoskeleton.
	In the deutrostome, the blastopore develops into an anus.
	Because echinoderms and chordates are deuterostomes, the two phyla may be related.

30.2    Structure and Function in Echinoderms

	Echinoderms are radially symmetrical and have a five-part body plan.
	They are slow moving and sessile.
	They also don't have a brain or head.
	The water vascular system is a network of fluid-filled tubes that enable the sea star to move.
	Tube feet are external structures of the water vascular system.
	Ampulla - muscular sac that helps force water through the water vascular system.
	When muscles in ampulla contract, water is forced into the tube feet, causing them to extend.
	Echinoderm's body is supported by an outer layer of smooth skin covered by hardened calcium plates.
	Most sea stars are carnivorous and often feeds on mollusks, coral polyps, and other echinoderms.
	As soon as shell opens, sea star pushes lower stomach out thru mouth and into the open shell.
	A sea star can push its stomach into a bivalve thru an opening 0.1 mm wide.
	A nerve ring surrounds the mouth.
	Nerve ring coordinates movement by receiving signals from receptor cells and sending impulses to muscles and tube feet.
	Sea stars can easily regenerate lost body parts.
	Echinoderms may have evolved from free-swimming, bilaterally symmetrical ancestors.

30.3    Echinoderm Diversity

	The brittle star and basket star are members of class Ophiuroidea.
	The arms of basket stars are highly branched.
	Spines on arms increase traction, much like tire treads help tires grip pavement.
	Both sand dollars and sea urchins are radially symmetrical.
	Sea cucumber is one of few echinoderms that has bilateral symmetry.

30.4    Invertebrate Chordate

	Notochord - firm but flexible tube located just below the nerve tube.
	Gill slits or pouches - original function was feeding.
	Post anal tail - during development, all chordates have a tail that reaches beyond the anus.
	Lancelets can swim, but spend most of their time buried in sand with just head exposed.
	Sea squirt, or tunicates belong to subphylum Urochodata.
	Tunicates are named for their leathery outer covering called a tunic.

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