ANIMAL DIVERSITY-Lecture outline[1]


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ANIMAL DIVERSITY Poriferans have a relatively simple, porous body Sponges are simple, sedentary animals without true tissues Water is drawn in through pores in the body wall into a central cavity, and then flows out through a larger opening Sponges have two cell layers The body of a sponge consists of two layers of cells separated by a gelatinous region Flagellated cells move water through the spongocoel , whose cells filter and engulf food by phagocytosis. Amoebocytes wander through the middle body region and produce spicules (skeletal fibers) Sponges have a relatively simple, porous body Sponges are suspension feeders , filtering food particles from water passed through food-trapping equipment To grow by 100 g, a sponge must filter 1,000 kg (1000 liters) of water Adult sponges can re-aggregate after being screened through a sieve! Sponges can reorganize themselves even after being put through a strainer After being pushed through a mesh, the cells reaggregate and reform a normal sponge. Only cells of the same species re-associate. The cell surfaces have receptor sites that are unique to each species of sponge. Cnidarians are radial animals with tentacles and stinging cells Cnidarians have two tissue layers: an outer epidermis and an inner cell layer lining the digestive cavity A jelly-filled middle region may have scattered amoeboid cells Cnidarians use tentacles to capture prey and push them into their mouths The mouth leads to the gastrovascular cavity , which functions in digestion Cnidoblasts on tentacles sting prey and function in defense Cnidarians have two kinds of radially symmetrical body forms The jellyfish-like medusa is free swimming and reproduces sexually The hydra-like polyp is sessile (attached to the bottom) and reproduces asexually
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Some cnidarians have alternating polyp and medusa forms in their life cycle, while others exist only as polyp or medusa forms The ancestor of animals was probably a colonial, flagellated protist Cnidarians kept this simple body plan. The Cambrian “Explosion”
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