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ANIMAL_LECTURE_SET_2009

ANIMAL_LECTURE_SET_2009 - Eumetazoans All animals except...

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All animals except sponges belong to the Eumetazoa, the animals with true tissues. The oldest eumetazoan clade is the Radiata, animals with radial symmetry and diploblastic embryos. The two phyla of Radiata, Cnidaria and Ctenophora, may have had separate origins from different protozoan ancestors. Eumetazoans
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Key terms to know by the end of this presentation: Radial symmetry diploblastic Nematocysts tissue grade of organization Polyp gastrodermis Medusa Oral end Aboral end Tentacle Manubrium
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The cnidarians (hydras, jellies, sea anemones, and coral animals) have a relatively simple body construction. They are a diverse group with over 10,000 living species, most of which are marine. The basic cnidarian body plan is a sac with a central digestive compartment, the gastrovascular cavity . Phylum Cnidaria: Cnidarians have radial symmetry, a gastrovascular cavity, and cnidocytes
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Major difference between the classes is which of the two body plans is present or dominant There are also other morphological distinctions you will see in the laboratory Phylum Cnidaria: Composed of Three Classes
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This basic body plan has two variations: the sessile polyp and the floating medusa. The cylindrical polyps , such as hydras and sea anemones, adhere to the substratum by the aboral end and extend their tentacles, waiting for prey. Medusas (also called jellies) are flattened, mouth-down versions of polyps that move by drifting passively and by contacting their bell-shaped bodies . Fig. 33.4
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Muscles and nerves exist in their simplest forms in cnidarians. Cells of the epidermis and gastrodermis have bundles of microfilaments arranged into contractile fibers. True muscle tissue appears first in triploblastic animals. When the animal closes its mouth, the gastrovascular cavity acts as a hydrostatic skeleton against which the contractile cells can work. Movements are controlled by a noncentralized nerve net associated with simple sensory receptors that are distributed radially around the body.
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Class Hydrozoa (hydro= water, zoon = animal) Hydra Gonionemus Obelia Physalia Phylum Cnidaria: Composed of Three Classes
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Solitary or colonial animals Polyp is the dominant stage Medusa stage is absent or reduced Medusae (when present) has a velum (iris-like diaphragm that is used to create a powerful jet for movement) Freshwater or marine Class Hydrozoa
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Fig. 33.5
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Nerve nets in cnidarians
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Hydra has unusual sexual structures for a cnidarian Male hydras produce sperm in spermaries-- small conical outgrowths from the side of the body Females have ova in their ovaries (more rounded in shape) Sperm are released travel through water to ovaries embryo develops in female ovary after 7-10 days young, miniature hydra is released.
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