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23.3 Sponges and Cnidarians KEY CONCEPT Sponges and cnidarians are the simplest animals. 23.3 Sponges and Cnidarians Phylum Porifera • Examples/Groups sponges • Characteristics: 1. Porifera means “pore bearer” 2. sponges are the most primitive animals on Earth http://www.youtube.com/watch?v=RmPTM965-1c&feature=related 23.3 Sponges and Cnidarians Phylum Porifera 3. are sessile = remain attached to surface; do not move 4. have specialized cells but no tissues 5. are filter feeders 23.3 Sponges and Cnidarians • Reproduction: – asexually – through budding and fragmentation 23.3 Sponges and Cnidarians – sexually - most species are hermaphrodites = can produce both sperm and egg 23.3 Sponges and Cnidarians - internal fertilization: * the sperm from one sponge is released into the water and enters the pore of another sponge - the amoebocytes or archaeocytes carry the sperm to the egg 23.3 Sponges and Cnidarians Cnidarians • Examples/Groups jellyfish, sea anemones, corals, hydras 23.3 Sponges and Cnidarians • Characteristics: 1. Are named for the stinging cells on their tentacles which contain poison in a structure called nematocysts discharged nematocyst barbs coiled nematocyst 23.3 Sponges and Cnidarians 2. All have stinging tentacles in a circle around the mouth 3. No brain or nerves but a structure called a nerve net sends impulses to body parts gastrovascular cavity mouth mesoglea tentacle oral arms 23.3 Sponges and Cnidarians Cnidarians are the oldest existing animals that have specialized tissues. • Reproduction: – asexually by budding – sexually by external fertilization = egg and sperm unite in the water 23.3 Sponges and Cnidarians • Cnidarians have two body forms: 1. polyp * tube shaped with tentacles pointing upwards around the mouth * is sessile * Ex: sea anemone hydra jellyfish (larva stage) 23.3 Sponges and Cnidarians 2. medusa * umbrella shaped with tentacles pointing downwards around the mouth * is mobile * Ex: jellyfish In the medusa form of a jellyfish, the tentacles and mouth face downward. 23.3 Sponges and Cnidarians Reef-building corals (Cnidarians) - found in both shallow and deep waters - those in shallow waters survive through a symbiotic relationship with algae ~ the algae transfers food to coral and the coral provides a home to the algae - size of prey ranges from microscopic zooplankton to small fish (depending on the size of the coral); they also ingest dissolved organic particles
