Phylum Echinodermata The Echinoderms General Characteristics Means spiny

Phylum Echinodermata The Echinoderms

General Characteristics • Means “spiny skin” • Radially symmetrical • No sign cephalization –No concentration of sensory organs @ anterior end

I sure wish I could trade my spiney skin and radial symmetry for some cephalization

• Adults develop from bilaterally symmetrical larvae. –Suggests bilaterally symmetrical ancestors

Sea urchin

• All are deuterostomes (like chordates) –Anus forms from blastopore • Compare to prostomes –Mouth develops from blastopore

Hi. I’m a Blastula. This is my blastopore

• Most exhibit pentaradial symmetry –Body parts extend from center along five “spokes”

• Endoskeleton composed of calcium carbonate plates called ossicles –May be attached to spines or spicules protruding through skin

• Presence of watervascular system –Network of waterfilled canals inside body

• Tube feet are small movable extensions of the water vascular system –Aid in movement, feeding, respiration and excretion

Classification • 7000 species

• Six classes –Crinoidea –Ophiuroidea –Echinoidea –Holothuroidea –Asteroidea –concentricycloidea

Class Crinoidea • Members include sea lilies and feather stars • Members are called crinoids • Crinoid means “lily-like”

• Five arms extend from body to form up to 200 more arms • Tube feet filter organisms and detritus –Also aid in gas exchange

• Cilia transport food to mouth at base of arms • Mouth faces upward, unlike other echinoderms

Sea lilies • Most closely resemble echinoderm fossils • Sessile as adults • Attach via long stalk • Filter-feeder

Feather Stars • Can swim or crawl as adults

Class Ophiuroidea • Means “snake-tail” • Basket stars and brittle stars • Distinguished by long, narrow arms

• Arms allow for quickest movement of all echinoderms • Benthic • Feed by raking in food with arms or gathering with tube feet

Basket Stars • Arms branch repeatedly to form numerous coils • Arms resemble tentacles

Brittle Stars • So named because arms break off easily, then are regenerated

Class Echinoidea • Means “spinelike” • Sea urchins and sand dollars • Compact, rigid endoskeleton called a test

Sea Urchin • Tube feet used for locomotion • Feed by scraping algae with five teeth that surround mouth

• Jawlike structure of teeth and muscle called Aristotle’s lantern • Spines may be short and flat, long and thin, or wedge shaped

• Spines may be barbed or hollow and venom filled

Sand Dollars • Found in sandy neritic province • Shape is adaptation for shallow burrowing

• Short spines used for locomotion, burrowing, and to help clean itself • Tube feet capture plankton or detritus as it passes over or settles on their body

Class Holothuroidea • Means “water polyp” • Sea Cucumbers • Burrow into soft sediment

• Ossicles are small and unconnected • Tube feet surround mouth • Digests organic material found in sediment

Class Asteroidea • Means “starlike” • Sea stars or starfish • Live in coastal waters

• Economically important because is predator of bivalvia

Concentricycloidea • Sea daisies • discovered in 1986, have disk-shaped flat bodies and are less than 0. 39 in. (1 cm) in diameter. • The two known species were located on wood found in deep waters off the coasts of New Zealand the Bahamas.

• They have a water-vascular system, with tube feet on the body surface around the edge of the disk. • They have no obvious arms or mouth, and appear to absorb nutrients through the membrane surrounded their bodies.