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Tree of Life The tree of life according to Ernst Haeckel, 1891 How does Porifera fit in? Porifera 3 body types choanocytes cellular level of organization unknown common ancestor Blastula stage heterotrophic multicellular eukaryote Other animals How does Cnidaria fit in? Cnidaria Porifera Other animals 3 body types choanocytes cellular level of organization Blastula stage heterotrophic multicellular eukaryote unknown common ancestor Phylum Cnidaria Level of Organization Tissue • cells are organized into tissues and work together to accomplish physiological functions Tissue Layers Diploblastic = 2 germ layers • endoderm gastrodermis • ectoderm epidermis mesoglea • gelatinous matrix between the 2 layers epidermis gastrovascular cavity mesoglea gastrodermis 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 gastrodermis mesoglea epidermis aboral surface mouth Gastrovascular cavity 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 ** General Life Cycle Radial Symmetry - body parts are arranged concentrically around an oral-aboral axis oral aboral Nematocysts • specialized stinging organelles • found within cnidocytes (cells) • cnidocytes are located in epidermis A cnidocyte with a nematocyst within it 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 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 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 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 Physiology Reproduction Asexual – budding – longitudinal fission – pedal laceration (e.g. sea anemones) Physiology Reproduction Sexual – usually dioecious (separate sexes e.g. humans) – monoecious (both male + female gonads in 1 individual) – results in Planula larva Phylum Cnidaria Class Hydrozoa Class Scyphozoa Class Anthozoa Class Hydrozoa • medusa & polyp body forms Fire coral Class Hydrozoa • medusa & polyp body forms • most are colonial colonies are formed of individual zooids a single zooid 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 Class Hydrozoa - a sessile colony showing polymorphism gonozooid entire colony gastrozooid Class Hydrozoa - a Portugese Man-o-war is a floating hydrozoan colony showing polymorphism pneumatophore entire colony gastrozooid dactylzooid Class Hydrozoa- life cycle sexual reproduction asexual reproduction Class Hydrozoa • Hydra is an example of a solitary, freshwater hydrozoan asexual reproduction sexual reproduction gonads bud Class Scyphozoa • “true” jellyfish • medusa & polyp body forms • thick mesoglea Class Scyphozoa- life cycle sperm egg ephyra strobila Adult medusa scyphistoma larva Class Anthozoa • polyp body form ONLY • all marine Class Anthozoa • some are colonial colonies are formed of individual zooids • some are solitary Class Anthozoa Sea anemones Class Anthozoa Soft Corals Sea pen Sea pansy Class Anthozoa Stony Corals Class Anthozoa- life cycle Sexual reproduction sperm egg larva Class Anthozoa- life cycle asexual reproduction fission pedal laceration fission How does Cnidaria fit in? Cnidaria 3 classes:Hydrozoa, Scyphozoa, Anthozoa Porifera 2 body types: polyp, medusa diploblastic 3 body types tissue level choanocytes of organization cellular level of organization Blastula stage heterotrophic multicellular eukaryote unknown common ancestor 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 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 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 Importance of Coral Reefs • one of the most productive ecosystems although the water is nutrient-poor • “hot spots” for biodiversity 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)
