worms - Worms - Platyhelminthes, Nematoda, Annelida -...

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Worms - Platyhelminthes, Nematoda, Annelida - numerous animal phyla are worms of one kind or another. We are only looking at three phyla of “worms”. - also, we are NOT going in taxonomic order in what follows. Usually, many more groups are covered before getting to the Annelids or Nematodes (your book turns everything upside down here). Phylum Platyhelminthes - Flat worms (12,000 species) [Fig. 33.10, p. 675] - Bilateral symmetry. - this is often a result of moving in one direction, thus having a “head” end. - flattened dorso-ventrally (thin from front to back). - anatomical terms - learn them (see the start of the pig dissection in the lab manual for more terms). - have mesoderm, and are generally much more complicated than cnidarians, but still fairly primitive for animals (all higher animals have three layers). - gut (if present) only has a single opening. - acoelomate (no body cavity) - have distinct organs and organ systems (e.g., digestive, nervous, reproductive, etc. [but NO circulatory system!]) Classes you need to know [TABLE 33.2, p. 674] Turbellaria - Planarians and similar. [similar to Fig. 33.9, p. 675] - mostly marine and free living. Carnivorous. - have a simple excretory system to remove nitrogenous wastes (flame cells, more later in the semester). - finely divided gastrovascular cavity (brings food to all parts, and allows for better digestion). - move by using several different muscle groups (working against a hydrostatic skeleton), or by using cilia (hence “turbellaria). - simple brain, eye-spots. Even show some learning ability.
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- reproduce asexually through regeneration, or sexually (hermaphroditic). Monogenea - flukes, mostly ectoparasites of fish.
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worms - Worms - Platyhelminthes, Nematoda, Annelida -...

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