Sponges

1. Protostomes Sponges Cnidarians Lophotrochozoa primitive flatworms Ecdysozoa Deuterostomes are different from protostomes due to basic features of how the zygote forms a multicellular embryo Deuterostomes

2. Embryonic Development: Early Cleavage Zygote Protostomes Deuterostomes • Spiral, • Determinate • Cleavage • developmental • fate is set early • - each cell has • specific destiny • Radial, • Indeterminate • Cleavage • each cell can • develop into a • complete embryo 2 cells 4 cells 8 cells view from above

3. Protostome Deuterostome GASTRULA STAGE of embryo Fate of Blastopore 1st opening of embryo becomes either the larval mouth or anus Coelom Formation ball of mesoderm cells hollows out versus space pinches off from embryo’s gut

4. Comparison of 2 major animal lineages Protostomes Deuterostomes - radial cleavage - cell fate is indeterminant (flexible; twins possible) - blastopore becomes anus - coelom develops from pinched-off gut space - dorsal nerve chord - spiral cleavage - cell fate is determinant (fixed) - blastopore becomes mouth - coelom develops from hollow ball of mesoderm - ventral nerve chord

5. 7,000 species Phylum Echinodermata Deuterostomes with penta-radial (5-fold) symmetry as adults - body organized along oral-aboralaxis (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)

6. Aboral (top) surface Oral (bottom) surface Madreporite, opening to water vascular system arm grooves(open on sea stars) mouth central disc body ray tube feet line open grooves

7. Endoskeleton Echinoderms 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

8. Phylum Echinodermata Class Asteroidea - sea stars Class Ophiuroidea - brittle stars & basket stars Class Holothuroidea - sea cucumbers Class Echinoidea - sea urchins & sand dollars

9. Class Asteroidea – sea stars - Body has 5 or morearms 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

10. Water Vascular System eachtube foot has its own bulb of fluid extends around central disc -may produce coelomocytes

11. Water Vascular System • Seawater enters through madreporite (opening on top), • mixes with coelom fluid • - fluid gets pushed into a tube footwhen 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

12. Sea stars use their tube feet to pull open shells of bivalves such as mussels, clams - then turntheir stomach inside-out, into the shell - digest the soft bivalve tissue inside its own shell sea star hunched over a mussel, ready to start pulling its shell open Stomach of the bat star Asterina pushed out against glass

13. Ecological Role of Sea Stars Pisaster sea stars are important local keystone predators in intertidal habitats - eat mussels, which are dominant competitorsfor space - maintain biodiversity by preventing mussels from taking up all available space & crowding everything else off the rocks

14. 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

15. Regeneration Sea 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?...

16. Phylum Echinodermata Class Asteroidea - sea stars Class Ophiuroidea - brittle stars Class Holothuroidea - sea cucumbers Class Echinoidea - sea urchins & sand dollars

17. Class Ophiuroidea – brittle stars • 5 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

18. Phylum Echinodermata Class Asteroidea - sea stars Class Ophiuroidea - brittle stars Class Echinoidea - sea urchins & sand dollars Class Holothuroidea - sea cucumbers

19. 1,000 species Class Echinoidea – Sea Urchins Ossicles fuse into a solid shell, under epithelium (= skin) - moveable spinesalso 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 Lanternused for scraping algae  important herbivores (feed on kelp) Pluteuslarva has bilateral symmetry, 8 arms “purps” Strongylocentrotus purpuratus

20. spines are a key adaptation: physical defense against predation

21. spine epithelium pencil urchin shell Urchin spines 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

22. Ecology of Urchin Barrens Urchins 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

23. 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

24. Diadema is a large, long-spined urchin - over 90% in Caribbean wiped out by mystery plague in 80’s 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

25. Diadema is a very 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

26. Phylum Echinodermata Class Asteroidea - sea stars Class Ophiuroidea - brittle stars Class Echinoidea - sea urchins & sand dollars Class Holothuroidea- sea cucumbers

27. 1,100 species 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 rows of tube feet

28. 1,100 species 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 rows of tube feet

29. 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!

30. 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

31. Echinoderm larvae Pluteus larvae of urchins and brittlestars 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 pluteus larva sea star larva