Biology Chapter 33 Objectives

Biology Chapter 33 Objectives - Chapter 33 Invertebrates...

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Chapter 33 Invertebrates Sponges 1. Water passing through porocytes enters a cavity called the spongocoel. Water enters the epidermis through channels formed by porocytes, doughnut-shaped cells that span the body wall. The epidermis is the outer layer, which consists of tightly packed epidermal cells. The spongocoel is lined with feeding cells called choanocytes. By beating flagella, the choanocytes create a current that draws water in through the porocytes. The wall of the sponge consists of two layers of cells separated by a gelatinous matrix, the mesohyl. Amoebocytes transport nutrients to other cells of the sponge body and also produce materials for skeletal fibers. Spicules are skeletal fibers. The spongocoel flows out of the sponge through a larger opening called the osculum. Eumetazoa 2. The animals in the phylum Cnidaria have radial symmetry, a gastrovascular cavity, and cnidocytes. The basic body plan of a cnidarian is a sac with a central digestive compartment, the gastrovascular cavity. A single opening to this cavity functions as both mouth and anus. Cnidarians are carnivores that use tentacles arranged in a ring around their mouth to capture prey and to push the food into their gastrovascular cavity, where digestion begins. The tentacles have cnidocytes on them, which are unique cells that function in defense and the capture of prey. 3. The cnidocytes on the tentacles function in defense and the capture of prey. They contain cnidae called nematocysts that are stinging capsules. Other cnidae have very long threads that stick to or entangle small prey that bump into the tentacles. When a "trigger" is stimulated by touch or by certain chemicals, the thread shoots out, puncturing and injecting poison into prey. 4. Sessile polyps are cylindrical forms that adhere to the substrate by the aboral end of the body and extend their tentacles, waiting for prey. Some examples are the hydra and the sea anemone. A floating medusa is a flattened, mouth-down version of the polyp. It moves freely in the water by a combo of passive drifting and contractions of its bell-shaped body. An example is the free-swimming jelly. 5. The four classes of Cnidaria include: 1) Hydrozoans which alternate between an asexually reproducing polyp and a sexually reproducing medusa form. Common hydras exist only in the polyp form. 2) Scyphozoans have a medusa stage that is more prevelent. The sessile polyp stage often does not occur in the jellies of the open ocean. 3) Cubozoans have a box-shaped medusa stage and complex eyes in the fringe of their medusae. Many species, such as the sea wasp, have highly toxic cnidocytes. 4) Anthozoans contain sea anemones and corals that only occur as polyps.
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Bilateria 6. a) Diplobastic development is when the animal forms only an ectoderm and an endoderm. Triploblastic development is when the animal produces a middle layer, the mesoderm, fromwhich arise muscles and other organs. b) Coelamates are any animal with a true coelaom. Acoelomates are triploblastic
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This note was uploaded on 08/29/2009 for the course BIOL 101 taught by Professor Sakji during the Fall '08 term at Linn Tech.

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Biology Chapter 33 Objectives - Chapter 33 Invertebrates...

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