Phylum Echinodermata

Phylum Echinodermata

About 7,000 species Strictly marine, mostly benthic. Typical deuterostomes.

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.

Ambulara C and D are the bivium, A B and E are the trivium.

What do Echinoderms look like?

Epidermis covers entire body. Endoskeleton of ossicles with

tubefeet and dermal branchia protruding through and 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? Water vascular system

Fluid-filled canals for internal transport and locomotion.

Fluid similar to sewater but has coelomcytes and organic molecules.

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. Also has Polian vessicles

(maintain internal pressure) and Tiedemann’s bodies (produce coelomcytes).

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? Support Calcareous endoskeleton with different degrees of calcification. Holothuroids have very muscular body walls.

How do Echinoderms support themselves and move? Movement

How do Echinoderms support themselves and move? Movement

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

Sand dollars use spines to burrow in sand.

How do Echinoderms support themselves and move? Nervous system Decentralized without cerebral ganglia. Relatively simple receptors: chemoreceptors, statocysts, touch. Some brittle stars have sclerites that act as tiny lenses across their

dorsal surface and work together as one giant lens.

How do Echinoderms feed and digest? s

How do Echinoderms feed and digest? Asteroids Most are predators and scavengers. Eversible portion of stomach

(cardiac stomach) extruded onto or into prey.

How do Echinoderms feed and digest? Asteroids Mouth ---> cardiac stomach ---> pyloric stomach ---> pyloric ducts

---> pyloric cecae ---> intestine ---> anus

How do Echinoderms feed and digest?

How do Echinoderms feed and digest? Echinoids Herbivores, suspension feeders, detritovores. Urchins have Aristotle’s lantern. Hard plates and muscles that

control protraction of five teeth. Teeth scrape algae off rocks and take

bites of macroalgae. Can excavate holes in rocks.

How do Echinoderms feed and digest? Echinoids Digestive mouth system ---> esophagus out of Aristotle’s lantern --->

long intestines ---> rectum ---> anus.

How do Echinoderms feed and digest? Holothuroids Suspension and deposit feeders. Extend mucus-covered buccal tentacles into water. Tentacles are

pushed into mouth one at a time. Mouth ---> esophagus ---> long intestines ---> rectum ---> anus.

How do Echinoderms feed and digest? Holothuroids Cuverian tubules - blind sticky tubes at base of respiratory tree.

Entangle predators. Evisceration.

How do Echinoderms maintain homeostasis? Circulation Internal transport by coeloms, water vascular system, and hemal

systems. Hemal system - array of canals and spaces enclosed within coelomic

channels called perihemal sinuses. Parallels water vascular system. Probably helps distribute respiratory gases and nutrients.

How do Echinoderms maintain homeostasis? Gas exchange Across podia and dermal gills (dermal

branchia). Countercurrent exchange.

How do Echinoderms maintain homeostasis? Gas exchange

How do Echinoderms maintain homeostasis? Gas exchange Holothuroids have respiratory trees. Water is actively pumped

by muscular hind end. Gases picked up by coelom and hemal system.

How do Echinoderms maintain homeostasis? Osmoregulation Osmoconformers. Waste is usually ammonia lost across podia and dermal

branchia.

How do Echinoderms reproduce and develop? Asexual reproduction Most capable of regenerating lost parts. Holothuroids

regenerate intestines and respiratory trees. Asteroids and ophiuroids regenerate lost arms and suckers.

How do Echinoderms reproduce and develop? Sexual reproduction Most gonochoristic. Gonads housed in genital sinuses. In classes with multiple

gonads, each has own gonopore in an interambulacral area.

How do Echinoderms reproduce and develop? Sexual reproduction Free spawning with indirect development to brooding with

direct development.

How do Echinoderms reproduce and develop? Sexual reproduction Isolecithal egg with small amount of yolk. Radial holoblastic cleavage ---> coeloblastula --->

coelogastrula by invagination ---> blastopore becomes anus ---> coelom formation by enterocoely ---> embryo becomes bilaterally symmetrical and develops into a larva.

Vitellaria of crinoid

Bipinnaria and brachiolaria of seastars

How do Echinoderms reproduce and develop? Sexual reproduction Isolecithal egg with small amount of yolk. Radial holoblastic cleavage ---> coeloblastula --->

coelogastrula by invagination ---> blastopore becomes anus ---> coelom formation by enterocoely ---> embryo becomes bilaterally symmetrical and develops into a larva.

Echinopluteus of urchin.

Aricularia of sea cucumber