Understanding Cnidaria: Physiology, Reproduction, and Life Cycle Stages

1. Tree of Life The tree of life according to Ernst Haeckel, 1891

2. How does Porifera fit in? Porifera 3 body types Other animals choanocytes cellular level of organization Blastula stage heterotrophic multicellular eukaryote unknown common ancestor

3. How does Cnidaria fit in? Cnidaria Porifera Other animals 3 body types choanocytes cellular level of organization Blastula stage heterotrophic multicellular unknown common ancestor eukaryote

4. Phylum Cnidaria

5. Level of Organization Tissue • cells are organized into tissues and work together to accomplish physiological functions

6. Tissue Layers • Diploblastic = 2 germ layers • endoderm  gastrodermis • ectoderm  epidermis • mesoglea • gelatinous matrix between the 2 layers gastrovascular cavity epidermis mesoglea gastrodermis

7. General Body Plan • sac-like body (only 1 opening) • Food and waste go in/out the same opening •  no anus! • water within GVC acts as a hydrostatic skeleton oral surface mouth gastrodermis Gastrovascular cavity mesoglea epidermis aboral surface

8. General Body Forms 2 different body forms are usually present in the life cycle: polyp & medusa ** one animal may pass through both forms during its life **

9. General Life Cycle

10. Radial Symmetry • - body parts are arranged concentrically around an oral-aboral axis oral aboral

11. Nematocysts • specialized stinging organelles • found within cnidocytes (cells) • cnidocytes are located in epidermis A cnidocyte with a nematocyst within it

12. Nematocysts • nematocysts are like “mini-harpoons” • cnidocil senses movement & acts like a “trigger” • can inject poison, coil around prey, or be adhesive • functions: • - prey capture; defense nematocyst cnidocil cnidocyte Undischarged Discharged

13. Colony formation • colony formation is common (colonial animals) • occurs via asexual reproduction (e.g. fission) • individual polyps are connected to one another by the GVC individual polyp

14. Physiology Feeding • nematocysts within cnidocytes • tentacles Digestion • extracellular (in GVC) • intracellular (by gastrodermal cells) • incomplete system (no anus) Gas exchange & Excretion • these systems are absent

15. Physiology Nervous System • nerve net (no central nervous system= no brain) • sense organs • statocysts (equilibrium organs) • ocelli (photosensitive organs) Skeletal System • water in GVC acts as a hydrostatic skeleton

16. Physiology Reproduction Asexual • budding • longitudinal fission • pedal laceration (e.g. sea anemones)

17. Physiology Reproduction Sexual • usually dioecious (separate sexes e.g. humans) • monoecious (both male + female gonads in 1 individual) • results in Planula larva

18. Phylum Cnidaria Class Hydrozoa Class Scyphozoa Class Anthozoa

19. Class Hydrozoa • medusa & polyp body forms Fire coral

20. Class Hydrozoa • medusa & polyp body forms • most are colonial •  colonies are formed of individual zooids a single zooid

21. Class Hydrozoa • many of these colonies show polymorphism •  this is where there are several different types of polyps/zooid and each type is specialized for a different function • e.g. gastrozooids = feeding polyps • e.g. dactylzooids = defense polyps •  all the zooids within a colony are genetically identical •  these different zooids work together in the colony

22. Class Hydrozoa - a sessile colony showing polymorphism gonozooid entire colony gastrozooid

23. Class Hydrozoa - a Portugese Man-o-war is a floating hydrozoan colony showing polymorphism pneumatophore entire colony gastrozooid dactylzooid

24. Class Hydrozoa- life cycle sexual reproduction asexual reproduction

25. Class Hydrozoa • Hydra is an example of a solitary, freshwater hydrozoan asexual reproduction sexual reproduction gonads bud

26. Class Scyphozoa • “true” jellyfish • medusa & polyp body forms • thick mesoglea

27. Class Scyphozoa- life cycle sperm egg ephyra Adult medusa strobila scyphistoma larva

28. Class Anthozoa • polyp body form ONLY • all marine

29. Class Anthozoa • some are colonial •  colonies are formed of individual zooids • some are solitary

30. Class Anthozoa Sea anemones

31. Sea pansy Class Anthozoa Soft Corals Sea pen

32. Class Anthozoa Stony Corals

33. Class Anthozoa- life cycle Sexual reproduction sperm egg larva

34. Class Anthozoa- life cycle asexual reproduction fission pedal laceration fission

35. How does Cnidaria fit in? Cnidaria 3 classes:Hydrozoa, Scyphozoa, Anthozoa Porifera 2 body types: polyp, medusa diploblastic 3 body types tissue level of organization choanocytes cellular level of organization Blastula stage heterotrophic multicellular unknown common ancestor eukaryote

36. Symbiosis Mutualism – • Corals contain endosymbiotic algae called zooxanthellae • the zooxanthellae photosynthesize and provide food for the coral while the coral provides a safe home zooxanthellae

37. Symbiosis Mutualism – • Many species of anemone fish (clown fish) live within anemones and are immune to their stinging nematocysts • the fish may lure in other fish for the anemone to capture and eat, while the anemone provides protection and a home

38. Coral Reefs • What are they? • stony corals lay down a calcium carbonate skeleton • these skeletons are laid down on top of one another and over thousands of years, form large calcium carbonate structures • these large structures, along with the plants and animals that inhabit them, are known as coral reefs • Where do they form? • in optimal conditions for their zooxanthellae •  shallow, warm, nutrient-poor waters

39. Importance of Coral Reefs • one of the most productive ecosystems although the water is nutrient-poor • “hot spots” for biodiversity

40. Threats to Coral Reefs • over-enrichment of nutrients from sewage and agricultural run-off • overfishing of herbivorous fish • global warming (leads to coral bleaching where corals expel their zooxanthellae)