Section 3: Sponges and cnidarians were the first animals to evolve from a multicellular ancestor. K What I Know W What I Want to Find Out L What I Learned
Vocabulary Review diploid New filter feeder sessile cnidocytes nematocyst gastrovascular cavity nerve net polyp medusa
Sponges Sponges have no tissues, no organs, and most lack symmetry. You can break a sponge down into individual cells and those cells will reform a new sponge. Sponges are in phylum Porifera.
Sponges Body structure Sponges are composed of two layers of independent cells with a jellylike substance in-between. Have a mouth-like opening at the top called an osculum.
Sponges Feeding and digestion Sponges are filter feeders that obtain food by filtering small particles out of the water. Sponges have free-swimming larvae, but are sessile, or attached to stay in one place, as adults. Food particles cling to the cells, and digestion of nutrients takes place within individual cells.
Sponges Support Within the jellylike substance between a sponge s two cell layers are archaeocytes. Archaeocytes are amoeba-like cells that can secrete spicules, the support structures of sponges Also involved in digestion, egg and sperm production, and excretion.
Sponges Sponge diversity Sponges placed into three classes based on the type of support system they have. Demospongiae: have spicules composed of spongin fiber, silica, or both Calcarea: spicules are composed of calcium carbonate Hexactinellida: spicules of silica joined together to form a netlike skeleton
Sponges Response to stimuli Sponges do not have nervous systems Have epithelial-like cells that detect external stimuli, such as touch or chemical signals Respond by closing their pores.
Sponges Reproduction Some sponges reproduce asexually Fragmentation Buddying Gemmules sponge cells protected by spicules
Sponges Reproduction Most sponges reproduce sexually Eggs remain within a sponge. Sperm are released into the water. After fertilization, the zygote develops into a free-swimming larva.
Sponges Sponge ecology Sponges are food for some tropical fishes and turtles. Also form habitats for a variety of worms, fishes, shrimp, and symbiotic green algae. Sponges are also beneficial to humans Spongin fiber sponges are used for household scrubbing purposes Potential use in pharmaceutical products
Cnidarians The phylum Cnidaria contains jellyfish and sea anemones Contains about 10,000 species, mostly marine
Cnidarians Body structure One body opening and most have two layers of cells Cell layers organized into tissues Outer layer provides protection, inner layer digestion Exhibit radial symmetry
Cnidarians Feeding and digestion Tentacles are armed with stinging cells called cnidocytes. Cnidocytes contain nematocysts, a capsule that holds a coiled tube containing poison and barbs. Nematocysts work like tiny harpoons in response to being touched or a chemical stimulus one of the fastest cellular processes in nature
Cnidarians Feeding and digestion After capture by nematocysts and tentacles, prey is brought to the mouth. Inner cell layer surrounds the gastrovascular cavity, where cells release digestive enzymes. Undigested materials are ejected through the mouth.
Cnidarians Response to stimuli Cnidarians have a nerve net that conducts impulses to and from all parts of the body. The impulses cause contractions of muscle-like cells in the two cell layers.
Cnidarians Reproduction Cnidarians have two body forms: a polyp and a medusa Polyps are tube-shaped with a mouth surrounded by tentacles Medusas are umbrella-shaped bodies with tentacles hanging down
Cnidarians Cnidarian diversity Four main classes of cnidarians: Hydroids: both polyp and medusa stages; many form colonies Jellyfishes: medusa is dominant body form; float near the surface of the ocean water Sea anemones and corals: polyp stage is dominant
Cnidarians Cnidarian ecology Mutualism is common in cnidarians Habitat for fishes Beneficial to humans Recreational pleasure from visiting coral reefs Medical use
Cnidarians Evolution of cnidarians Scientists question whether the ancestral cnidarian had a polyp or medusa body form.
Review Essential Questions What are the characteristics of sponges and cnidarians? How are sponges and cnidarians alike and different? What is the ecological importance of sponges and cnidarians? Vocabulary filter feeder sessile cnidocytes nematocyst gastrovascular cavity nerve net polyp medusa