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Unformatted text preview: Ch. 33 - Invertebrates Most Recent Hypothesis About Animal Phylogeny (Figure 33.11) I. Sponges are basal animals that lack true tissues A. Porifera: Phyla Calcarea and Silicea 1. Only organized at the cellular level - no tissues 2. Live in both fresh and marine waters 3. Lack true tissues and organs - organized at cellular level *4. Asymmetrical body plan - growth dependent on the environmental conditions B. Sponges 1. Sponges are suspension feeders a. Filter water passing through their bodies 2. Pores- doughnut shaped cells that span the body wall 3. Chanocytes- line the spongocoel, movement of flagella sets up water flow, trap food and ingest it by phagocytosis pass it along to ameobocytes 4. Ameobocytes- transport nutrients to other cells, secretes spicules 5. Spicules- skeletal elements that determine the structure *6. Path of water flow - pores >spongocoel>osculum II. Cnidarians are an ancient phylum of eumetazoans. A. Cnidarians 1. Wide range of sessile and floating forms including jellyfish, corals, and hydras *2. Simple diploblastic, radial body plan *a. Diploblastic- two tissue layers (outer epidermis and inner endodermis) *b. Body plan is a sac with a central gastrovascular cavity where food is digested c. Single opening serves as both mouth and anus (nutrients absorbed and waste deposited from same opening) d. Mesoglea layer between epidermis and endodermis (gastrodermis) B. Cnidarian Body Plans (Figure 33.5) 1. Polyp- form is generally sessile (immobile form) 2. Medusa- form moves freely in water by passive drifting and contractions of the bell (mobile form) 3. Both forms have endodermal and epidermal layer with mesoglea layer in between and have a gastrovascular cavity C. Defining Feature of Cnidarians 1. Cnidocytes- unique cells that function in defense and the capture of prey 2. Stimulus causes the cell to evert releasing thread 3. Some cnidocytes sting, others just entangle the prey a. Some of the most toxic species on the planet *D. Cnidarian Classes III. Lophotrochozoans, a clade identified by molecular data, have the widest range of animal body forms A. Most animals belong to the bilateral clade (Figure 33.2) *1. Bilateral symmetry (symmetric across only one plane), cephalization (nervous tissue becomes concentrated towards one end of the body, head) *2. Triploblastic development (tissue layers) a. Ectoderm - outer layer b. Mesoderm - middle c. Endoderm - inner B. Flatworms - Phylum Platyhelminthes 1. Live in marine, freshwater, and damp terrestrial habitats (some parasitic - live inside a host) *2. Triploblastic development, but aceolomate- lack body cavity (only have digestive cavity) 3. Class Turbellaria a. Most free living marine and freshwater worms b. Have: light-sensitive eyespots, centralized nerve net with anterior ganglia, and gastrovascular cavity with two-way pharynx 4. Class Trematoda a. Blood fluke, Schistosoma mansoni , life cycle: b. Doesn't cause much harm to humans unless hard coatings of eggs scratch intestines as they are passed C. TapewormsC....
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- Spring '08