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Phylum Porifera Porifera = pore bearers; they are sponges Sponges •About 15,000 species of sponges •Most marine; Some 150 species live in freshwater Characteristics • They are the simplest of multicellular animals. • Their bodies are an assemblage of cells embedded in a gelatinous mass and supported by a skeleton of minute needlelike spicules and proteins. • They are filter feeders that are attached to the bottom of a river or the sea. • They depend on currents to eat, and they depend on the currents to wash way their waste. Characteristics continued… • They have no organs or true tissues. They have no nervous systems. They have no sense organs. They can be 2 mm in size to 2 meters in size. They either have radial symmetry or no symmetry at all. Phylum Cnidarians Box jellyfish This phylum includes hydras, jellyfishes, sea anemones, and corals. They live alone or in colonies. Body Structure • They are soft-bodied, carnivorous animals, that have stinging tentacles arrange in circles around their mouths. • They are the simplest animals to have body symmetry and specialized tissues. They are a few cells thick and have simple body systems. • They are radially symmetrical and have a central mouth and tentacles. Stinging tentacles They use their stinging tentacles to capture prey and for defense. • They each have a nematocyst. This is a poison-filled, stinging structure that contains a tightly coiled dart. Reproductive • They have a two staged life cycle; they are polyps and medusas. • Polyps are the cylindrical body with tentacles. They don’t move. • The medusas are belled shaped body and motile. Reproduction They produce both sexually and asexually. Polyps can reproduce asexually by budding. In the Medusa form there is external fertilization. The male release sperm into the water and the female releases eggs into the water. Internal body structure.. • They have three layers: gastroderm (inner lining where digestion takes place), epidermis is the outer layer of cells, and the mesoglea that lies between the two. Feeding • Feeding – Stung by tentacles and pulled into the mouth Other systems • Circulatory, respiratory and excretion – All take place by diffusion. Movement and response • Response – Gather info by specialized sensory cells. They respond to touch and have primitive eyes, which see light. • Movement – Depends on the species. They most often move by jet propulsion.