4Differences between Classes Some spend more time in the medusa or polyp formCan reproduce differentlyCan be colonial or solitary
5Cnidaria Characteristics Symmetry: RadialLevel of Organization: TissueTwo cell layers (epidermis and gastrodermis) around a jelly-like substance (mesoglea)
6Feeding: Excretion: Suspension feeding Single opening (mouth/anus) into a gastrovascular cavityAll are carnivoresHave light sensing organs (ocelli)Excretion:Wastes diffuse out of the cells into the water
7Defense / Predation: Stinging Cells All Cnidarians have stinging cells to protect themselvesA nematocyst is triggered with a hair cellIt ejects a harpoon or string with a toxin
8Class AnthozoaCorals and anemonesdominant polyp life stage
9Anemones Solitary: Usually one large polyp Some can “swim” away if attackedSome have symbiotic relationships, e.g. with clownfish or shrimp
10Corals Corals are colonial animals Hard Corals Many polyps live on the outside of a calcium carbonate skeleton
11Soft CoralsMany polyps live together but without the hard skeleton
12Reproduction Both sexual and asexual reproduction Asexual reproduction budding or fission (splitting in two)Sexual reproductionSpawningFemale eject eggs and males eject sperm into the waterTimed to the phase of the moon!
20Special relationships with algae Coral animals have a symbiotic relationship with a kind of algae called zooxanthellaeMutualistic relationship – they both benefit one another
21ZooxanthellaeDoes photosynthesis and gives the coral food (90% of the coral’s food is from here!)Coralgives the zooxanthellae a stable homegives the zooxanthellae nutrients from its waste
22Colourful corals!The algae are responsible for the beautiful colours we see
23Coral bleachingZooxanthellae are very sensitive to temperature change and pollutionIf the temperature becomes too high, they leave the coralThis is coral bleaching.Without the zooxanthellae, the coral will die.