phylum echinodermata - aktifitasblog.ub.ac.id/gedeekodarmono/files/2013/05/echinodermata.pdf ·...

Phylum Echinodermata


About 7,000 species

Strictly marine, mostly benthic.

Typical deuterostomes.


Class Crinoidea (sea lilies)


Class Crinoidea

Class Asteroidea (sea stars)


Class Crinoidea

Class Ophiuroidea (brittle stars

and basket stars)

Class Asteroidea


Class Crinoidea

Class Echinoidea (sea urchins and

sand dollars)

Class Ophiuroidea

Class Asteroidea


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.


Oral and aboral surfaces.


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.


Epidermis covers entire body.

Endoskeleton of ossicles with

tubefeet and dermal branchia

protruding through and spines and

pedicellaria on outside.

Body wall


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


Tubercles and moveable spines on

skeletal plates of echinoids.

Small muscles attach spines to test.

Body wall


Pedicellaria in echinoids and asreroids.

Respond to external stimuli independent of

nervous system.

Keep debris and larvae from settling, protection,

hold on to material for camouflage.

Body wall


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.



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).



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.



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.



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.



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.


Movement

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

Asteroids crawl with tube feet.


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.


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?

Crinoids

Filter feed with oral side up and arms and pinnules outstretched.

Food particles brought to mouth via cilia in ambulacral grooves.

Mouth opens to short esophagus, to

long intestine, to anus.


Asteroids

Most are predators and scavengers. Eversible portion of stomach

(cardiac stomach) extruded onto or into prey.


Asteroids

Mouth ---> cardiac stomach ---> pyloric stomach ---> pyloric ducts

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


Ophiuroids

Predators, scavengers, filter feeders, deposit feeders.

Food collected and passed along podia and spines to mouth.

Digestive system reduced with no anus.


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.


Echinoids

Digestive mouth system ---> esophagus out of Aristotle’s lantern --->

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


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.


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.


Gas exchange

Across podia and dermal gills (dermal

branchia).

Countercurrent exchange.


Gas exchange

Ophiuroids have ten invaginations in the

body wall called bursae. Water circulated

by cilia.


Gas exchange

Holothuroids have respiratory trees. Water is actively pumped

by muscular hind end. Gases picked up by coelom and

hemal system.


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.


Sexual reproduction

Most gonochoristic.

Gonads housed in genital sinuses. In classes with multiple

gonads, each has own gonopore in an interambulacral area.


Sexual reproduction

Free spawning with indirect development to brooding with

direct development.


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


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.

Ophiopluteus of

brittle star Echinopluteus

of urchin.

Aricularia of

sea cucumber

phylum echinodermata - aktifitasblog.ub.ac.id/gedeekodarmono/files/2013/05/echinodermata.pdf ·...

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