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Bilaterally Symmetrical Worms

Bilaterally Symmetrical Worms. Platyhelminthes, Nemertea, Nematoda, Annelida, and 4 unique groups. Anatomical Sides of a Bilateral Organism. Anterior – front side of an organism where the head with a brain or nerve net is located

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Bilaterally Symmetrical Worms

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  1. Bilaterally Symmetrical Worms Platyhelminthes, Nemertea, Nematoda, Annelida, and 4 unique groups

  2. Anatomical Sides of a Bilateral Organism • Anterior – front side of an organism where the head with a brain or nerve net is located • Posterior – the rear side of an organism(really the only way to tell for sure is that it is the side opposite from the head region) • Dorsal – the back surface of an organism • Ventral – the underside or belly region of an organism

  3. Anatomical Sides of a Radial vs Bilateral Organism

  4. Phylum Platyhelminthes Characteristics: • have bilateral symmetry • have a vermiform (wormlike shape) • have a third layer of cells (the mesoderm) • The mesoderm produces muscular layers, an excretory system, and an elaborate reproductive system. • exhibit an acoelomate body plan

  5. Platyhelminthes Platyhelminthes vs Cnidarians Platyhelminthes are composed of 3 cell layers where as Cnidarians are only composed of 2 • ectoderm is responsible for the production of much of the sensory system and surface skin (among other things) • endoderm contributes to the growth of structures such as the lining of the gut • mesoderm is used to build muscular, excretory, and reproductive systems

  6. Platyhelminthes The increases in complexity compared to Sponges, Cnidarians, and Ctenophora have led to increases in mobility, higher activity, and general increase in responsiveness of the organisms from this phylum

  7. Platyhelminthes • Platyhelminths are commonly known as "flatworms," due to their almost paper-thin structure. • They have a incomplete digestive system – meaning they have only one opening for the mouth and the anus. • They typically undergo sexual reproduction but can also reproduce asexually by regeneration. • Most species are hermaphrodites (contain both male and female parts)

  8. 3 Major Classes of Platyhelminthes • TURBELLARIAN– free-living • TREMATODA – parasitic • CESTODA – parasitic

  9. CLASS TURBELLARIAN • 3000 species • most marine • ex. planaria (fresh water)

  10. CLASS TURBELLARIAN - Planarian • External anatomy • anterior end spade shaped • posterior end tapered • body covered with cilia • Movement • move by undulative motion or • laying down mucus layer and beating cilia • Digestion and excretion • scavenger (carrion) • predator (small prey)

  11. CLASS TURBELLARIAN - Planarian • Digestion • muscular pharynx extended out of mouth • food sucked in • passed into intestines (branched) • nutrients absorbed through intestinal wall or phagocytosis • undigested food excreted through pharynx and mouth • Excretion • chemical wastes and excess water eliminated by network of ducts (pores and canals) • contains flame cells • flame cells enclose a tuft of beating cilia • cilia moves wastes into the ducts -> • excretory pores - > out

  12. CLASS TURBELLARIAN - Planarian • Nervous control • organized • sense light intensity and direction • two anterior eyespots (photosensitive cells) • touch, taste, and smell receptors • two anterior ganglia (clusters of nerves) -> simple brain • capable of simple "learning" • memory stored chemically

  13. CLASS TURBELLARIAN - Planarian • Reproduction • hermaphrodites • sexual reproduction • simultaneous fertilization • protective encapsulated eggs stick to rock • hatch 2-3 weeks • Mating season is February – March • asexual (summer) • attach to rock surface with posterior end • stretch until they tear into two • each half regenerates lost parts

  14. CLASS TURBELLARIAN - Planarian

  15. CLASS TURBELLARIAN - Planarian

  16. CLASS TREMATODA • 6,000 species • parasitic - both endoparasites and ectoparasites • leaf shaped • eg. flukes

  17. CLASS TREMATODA - Fluke • parasites • 1 cm long (oval shaped) • 2 sucker mouths (anterior and ventral) • cling to host • anterior sucker sucks in blood, cells and fluids of host

  18. CLASS TREMATODA - Fluke • Nervous and Excretory system • Turbellarian like • Reproduction • complex reproductive life cycle • hermaphroditic • long coiled uterus (stores 10,000+ eggs) • eggs released through genital pore -> larvae

  19. TREMATODA – Fluke Life Cycle

  20. CLASS CESTODA • 1,500 species • Also known as TAPEWORMS • most are parasitic (7 in humans) • adapted for parasitic life • tough outer tegument • hooks and suckers

  21. CLASS CESTODA • nervous system extends length of body • lack sense organs, mouth, and digestive tract • absorb nutrients directly through heavily folded tegument knoblike head with hooks and suckers (scolex) • grows by producing body segments (proglottids) • oldest proglottids at posterior

  22. CLASS CESTODA • Life cycle and reproduction • proglottids contain both male and female reproductive organs • cross fertilization is typical between individuals or proglottids • after fertilization - proglottids break off and are eliminated with feces

  23. CLASS CESTODA

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