Phylum Echinodermata

Echinodermata • “Spiny Skin”

• Radially symmetrical in five ways (pentamerous)

Echinodermata • No head, right or left side, or top or bottom, so

we refer to the “oral surface” (mouth side) and the “aboral surface” (side without a mouth)

Echinodermata • Complete digestive tract

• Coelom

• Endoskeleton

• Water vascular system

• Tube feet

Echinodermata

Examples of Echinoderms • Sea Stars

Examples of Echinoderms • Brittle Stars

Examples of Echinoderms • Urchins

Examples of Echinoderms • Sand Dollars

Examples of Echinoderms • Sea cucumbers

Phylum Echinodermata

About 7,000 species Strictly marine, mostly benthic.

Phylum Echinodermata

Class Crinoidea (sea lilies)

Phylum Echinodermata

Class Crinoidea

Class Asteroidea (sea stars)

Phylum Echinodermata

Class Crinoidea

Class Ophiuroidea (brittle stars and basket stars)

Class Asteroidea

Phylum Echinodermata

Class Crinoidea

Class Echinoidea (sea urchins and sand dollars)

Class Ophiuroidea

Class Asteroidea

Phylum Echinodermata

Class Crinoidea

Class Holothuroidea (sea cucumbers)

Class Echinoidea Class Ophiuroidea

Class Asteroidea

What do Echinoderms look like?

Pentamerous radial symmetry. Oral and aboral surfaces. Oral surface has ambulacral grooves associated

with tubefeet called podia.

What do Echinoderms look like?

Oral and aboral surfaces.

What do Echinoderms look like?

Arms (ambulacra) numbered with reference to the madreporite. Ambulacrum opposite is A then proceed couterclockwise.

What do Echinoderms look like?

Epidermis covers entire body. Endoskeleton of ossicles with

tubefeet, spines and pedicellaria on outside.

Body wall

What do Echinoderms look like?

Ossicles can be fused into a test (urchins and sand dollars). Ossicles spread apart in cucumbers. Ossicles intermediate and variable in seastars. Muscle fibers beneath ossicles.

Body wall

What do Echinoderms look like?

Tubercles and moveable spines on skeletal plates of echinoids.

Small muscles attach spines to test.

Body wall

What do Echinoderms look like?

Pedicellaria in echinoids and asteroids. Respond to external stimuli independent of

nervous system. Keep debris and larvae from settling, protection,

hold on to material for camouflage, capture prey.

Body wall

What do Echinoderms look like?

Water vascular system

Fluid-filled canals for internal transport and locomotion.

Moved through system with cilia.

What do Echinoderms look like?

Water vascular system

Asteroidea: Madreporite on aboral surface. Grooved with ciliated epidermis. May

allow seawater into vascular system. Ampulla under madreporite connected to water vascular system and

hemal system. Stone canal connects ampulla to rest of system. Connects to ring canal. Ring canal leads to radial canals in each arm

What do Echinoderms look like?

Water vascular system

Radial canals lead to lateral canals which pass through pores in the skeletal plates and end in tube feet.

Each tube foot has an ampulla on top

and a suckered muscular podium on bottom.

Tube feet used for locomotion, prey capture, adherence to substratum.

Terminal tubefeet are chemosensory.

What do Echinoderms look like?

Water vascular system

Tube feet move by combination of muscles and hydraulics.

Valve at lateral canal that shuts and isolates the tubefoot.

Ampulla contracts and pushes fluid into the tubefoot to extend it.

Sucker pressed on substratum and sticks with adhesive secretions. Longitudinal muscles contract to raise middle of sucker to create a

vacuum. Also shortens podium, forcing water back into ampulla. For release, longitudinal muscles relax, ampulla contracts and water

forced back into podium. Suction released.

What do Echinoderms look like?

Water vascular system

Ophiuroids: Madreporite on oral surface. Tudefeet don’t have suckers.

Flexible used for feeding.

Crinoids: Water vascular system entirely

coelomic fluid. No madreporite, many stony canals.

Radial canals extend up each arm. Suckerless podia on branches called

pinnules.

What do Echinoderms look like?

Water vascular system

Echinoids: Madreporite on special plate around

aboral pole. Podia pass through holes in

ambulacral plates

Holothuroids: Madreporite internal and open to

coelom. Three rows of tube feet (trivium) on

“ventral” surface, two rows (bivium) on “dorsal” surface.

How do Echinoderms support themselves and move?

Movement

Crinoids walk on the tips of their arms. Some swim.

Asteroids crawl with tube feet.

How do Echinoderms support themselves and move?

Movement

Ophiuroids use flexible arms for crawling.

Urchins use tube feet and moveable spines.

Cucumbers crawl on podia of trivium or by muscular action of the body wall.

Sand dollars use spines to burrow in sand.