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BIOL 2030 (36)
Chapter 7


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BIOL 2030
German Reyes

CHAPTER 7 – Radiate Animals - Contain phyla Cnidaria and Ctenophora which have radial (good for sessile) or biradial symmetry Phylum Cnidaria - Have cells called cnidocytes which contain the stinging organelles (cnidae). Nematocysts is a kind of cnidae. - Mostly sessile or slow moving or slow swimming. Efficient predators - Five classes: Hydrozoa, Scyphozoa, Cubozoa, Anthozoa, and Staurozoa. - Are in forms of polyp or medusa - Have an incomplete gut (gastrovascular cavity) and no respiratory or excretory system - Asexual reproduction (budding) and sexual reproduction - There is dimorphism (polyp and medusa forms) and sometimes polymorphism (when a colony contains several body forms) displayed. Eg. Of polymorphism is class Hydrozoa - Some hydras move by bending over and attaching their tentacles to the substratum. - Life cycle: zygote turns into free-swimming planula larva. The planula settles and forms a polyp. The polyp may reproduce asexually or (in case of Hydrozoa and Scyphozoa) the polyp makes a medusa. Medusa reproduce sexually and are dioecious. - Extracellular digestion in gastrovascular cavity and intracellular digestion in gastrodermal cells - Polyp body wall: outer epidermis (contains gland cells, cnidocytes, sensory and nerve cells) , inner gastrodermis (lines with gastrovascular cavity), and mesoglea is in-between them. Water in gastrovascular cavity serves as hydrostatic skeleton. Class Hydrozoa - Live in colonial form and have both asexual polyp and sexual medusa stage. - Eg. Hydra, Obelia - Catch prey with tentacles and move it close to the mouth. The chemical glutathione causes the mouth to open - Sometimes, during budding, the bud do not detach from the parent and form a colony (not hydras, but Obelia). In Obelia gonangia is the reproductive polyps - Ocelli are light-sensitive organs. Statocysts: small organs of equilibrium Class Scypho
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