Sponges

Cnidarians

primitiveflatworms

Deuterostomes are different from protostomes due to basic features of how the zygote forms a multicellular embryo

Deuterostomes

Ecdysozoa

Protostomes

Lophotrochozoa

Spiral, Determinate Cleavage

- developmental fate is set early

- each cell has specific destiny

Radial, Indeterminate Cleavage

- each cell can develop into a complete embryo

Embryonic Development: Early Cleavage

Protostomes DeuterostomesZygote

2 cells

4 cells

8 cells

viewfrom

above

Fate ofBlastopore

CoelomFormation

Protostome DeuterostomeGASTRULA STAGE of embryo

1st opening of embryo becomes either the larval mouth or anus

ball of mesodermcells hollows out

versusspace pinches offfrom embryo’s gut

Comparison of 2 major animal lineages

DeuterostomesProtostomes

- spiral cleavage

- cell fate is determinant (fixed)

- blastopore becomes mouth

- coelom develops from

hollow ball of mesoderm

- ventral nerve chord

- radial cleavage

- cell fate is indeterminant

(flexible; twins possible)

- blastopore becomes anus

- coelom develops from

pinched-off gut space

- dorsal nerve chord

7,000 species

Deuterostomes with penta-radial (5-fold) symmetry as adults

- body organized along oral-aboral axis (mouth-to-anus)

- larvae are still bilaterally symmetric

Endoskeleton: hard parts inside of soft tissue (like our bones)

- bony ossicles (chunks) or plates develop from mesoderm

Water vascular system develops from coelom- powers movement, often using external tube feet

- important in local marine ecosystems as herbivores (urchins)

and keystone predators (sea stars)

Phylum Echinodermata

Aboral (top) surface Oral (bottom) surface

centraldisc

mouth

body ray tube feet line open grooves

arm grooves (open on sea stars)Madreporite, opening to water vascular system

EndoskeletonEchinoderms have an epidermis covering a calcium carbonate endoskeleton (= inner skeleton), derived from mesoderm

- skeleton is composed of ossicles, porous chunks of calcium carbonate filled with living tissue

Ossicles fuse together in sea urchins to form protective inner shell and spines

Class Asteroidea - sea stars

Class Ophiuroidea - brittle stars & basket stars

Class Holothuroidea - sea cucumbers

Class Echinoidea - sea urchins & sand dollars

Phylum Echinodermata

Class Asteroidea – sea stars- Body has 5 or more arms that flow into a central disc

- Arm grooves open, lined with tube feet provide suction for

holding onto rocks, opening bivalves

- feathery gills anywhere on body surface

Water Vascular System

extends aroundcentral disc

-may produce coelomocytes

each tube foot has itsown bulb of fluid

Water Vascular SystemSeawater enters through madreporite (opening on top), mixes with coelom fluid

- fluid gets pushed into a tube foot when its bulb contracts

(1) sucker is pushed flat against substrate

(2) muscles in tube foot contract, pushing fluid back out

(3) muscles pull up against the sucker, creating a vacuum this creates the suction which holds the foot to a rock

(4) suction is released when fluid is once again pushed into the tube foot’s sucker, relieving the vacuum

Sea stars use their tube feet to pull open shells of bivalves such as mussels, clams

- then turn their stomach inside-out, into the shell

- digest the soft bivalve tissue inside its own shell

Stomach of the bat star Asterina pushed out against glass

sea star hunched over a mussel,ready to start pulling its shell open

Pisaster sea stars are important local keystone predators in intertidal habitats

- eat mussels, which are dominant competitors for space

- maintain biodiversity by preventing mussels from taking up all available space & crowding everything else off the rocks

Ecological Role of Sea Stars

Crown-of-Thorns starfish, Acanthaster planci

- eats live coral polyps

- in recent decades, major outbreaks have resulted in massive coral loss in Australia; human influences suspected

RegenerationSea stars are famous for regenerating lost arms

- some can re-grow an entire body from one dropped arm !

Which is healing? which is asexual reproduction?...

Class Asteroidea - sea stars

Class Ophiuroidea - brittle stars

Class Holothuroidea - sea cucumbers

Class Echinoidea - sea urchins & sand dollars

Phylum Echinodermata

Class Ophiuroidea – brittle stars5 arms attached to central disc at flexible joints

- tube feet lack suckers; watch how they move using their arms

- hide under rocks; snake-like arms reach out to grab food

- ossicles form a “spine” of vertebrae down each arm

- arms bend side-to-side but not up/down: “brittle”stars because arms break off

Class Asteroidea - sea stars

Class Ophiuroidea - brittle stars

Class Echinoidea - sea urchins & sand dollars

Class Holothuroidea - sea cucumbers

Phylum Echinodermata

Class Echinoidea – Sea UrchinsOssicles fuse into a solid shell, under epithelium (= skin)

- moveable spines also covered in epithelium

- holes in shell let tube feet poke out [look for these in lab !]

- mouth on bottom; anus opens on top

Unique 5-sided tooth called

Aristotle’s Lantern used for

scraping algae important

herbivores (feed on kelp)

Pluteus larva has bilateral

symmetry, 8 armsStrongylocentrotus purpuratus

1,000 species

“purps”

spines are a key adaptation: physical defense against predation

Urchin spines

pencil urchin shell

spine

epithelium

In most urchins, spines are sharp and may contain toxins

spines of Tripneustes

In pencil urchins, spines are fat and blunt... urchin uses them to jam itself into holes so it can’t be pulled out

Ecology of Urchin BarrensUrchins eat kelp and other macroalgae

Urchins are eaten by sea otters, which are keystone predators

healthy ecosystem with plenty of algae left

lots of food for other animals

Ecology of Urchin Barrens

When predators are hunted down, urchin populations grow out of control

- quickly eat all available drift kelp falling onto sea floor; get hungry....

- urchins mobilize, march out of hiding places across sea floor

- graze down all available kelp, creating urchin barrens where there is no algae for other consumers lose biodiversity

removal of a keystone predator like the otter has cascading negative effects on diversity of an ecosystem

Corals became overgrown by algae in many places following Diadema die-off

- algae grew too fast for coral to compete, without the big urchins to graze down the algae

Diadema is a large, long-spined urchin

- over 90% in Caribbean wiped out by mystery plague in 80’s

Shrimp swarms used to hide among Diadema spines

- switched to aggressive damselfish (“farming fish”) when urchins died off

Diadema is a very long-spined urchin

- over 90% in Caribbean wiped out by mystery plague in 80’s

Class Asteroidea - sea stars

Class Ophiuroidea - brittle stars

Class Echinoidea - sea urchins & sand dollars

Class Holothuroidea - sea cucumbers

Phylum Echinodermata

Class Holothuroidea – Sea Cucumbers

Only echinoderm where body lies on its side

- tube feet on ventral (belly) side only

Feeding tentacles around mouth used to filter feed or eat sand

- organic matter digested, clean sand pooped out

1,100 species

rows of tube feet

Class Holothuroidea – Sea Cucumbers

Only echinoderm where body lies on its side

- tube feet on ventral (belly) side only

Feeding tentacles around mouth used to filter feed or eat sand

- organic matter digested, clean sand pooped out

1,100 species

rows of tube feet

Cucumber Defense

No spines – defend against predators by:

a) shooting defensive strings out of anus

b) spitting out intestines (regrow them later)

also breathe through their anus!

Cucumber Commensalism

Sea cucumbers may have commensal organisms, including a pearl-fish and a crab, living in their anus!

commensal = doesn’t hurt, but doesn’t help

Echinoderm larvae

Pluteus larvae of urchins andbrittlestars have bilateral symmetry

- show that echinoderms evolved from a typical bilaterian ancestor, but adult stage evolved a weird radial symmetry

4 pairs of cilia-covered arms

- catch one-celled algae, pass them along to mouth

- cilia also used to swim

sea star larvapluteus larva