sponges cnidarians primitive flatworms deuterostomes are different from protostomes due to basic...
TRANSCRIPT
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