6. Platyhelminthes I

6. Platyhelminthes I - REVIEW Life Cycle / Life History -...

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Unformatted text preview: REVIEW Life Cycle / Life History - series of stages which an organism passes Reproduction and Life Cycles/Life History e.g. Anthozoa Polyp only Metamorphosis Simple - one free living adult stage, no larval stages Complex - multiple free living adult and / or larval stages (differ in morphology) can be sexually or asexually produced can be 1n or 2n Benthic Polyp (2 n) male female meiosis gametes (n) gametes (n) asex. budding Planula Larva zygote (2 n) Scyphozoa Medusa Only Ephyra (pelagic) Medusa Strobila (benthic) Medusa - pelagic (2 n) male female Planula (benthic) meiosis gametes (n) gametes (n) Scyphistoma tiny – polyp like Ephyra Planula Larva zygote (2 n) Strobila Scyphistoma Hydrozoa Metagenesis Metagenesis Alternation of benthic polyp and pelagic medusa ! alternation of generations Heteromorphic Life History 2 different adult stages 1 asexual bud Asexual Reproduction Modes in Cnidaria Budding Fission Pedal Laceration Strobilation Benthic polyp (2 n) Pelagic Medusa (2 n) male female meiosis asex. budding Metamorphosis Sexual Reproduction Modes Hermaphroditic or Dioecious (2 sexes) External or Internal Fertilization Larvae Released (planktonic) or Brooded gametes (n) gametes (n) zygote (2 n) Planula Larva Phylum Ctenophora Cniarian Classes differ by Life History Anthozoa – polyp only (e.g., anemones, corals) Scyphozoa – medusa (e.g., true jelly fish) Hydrozoa – all three types, most show metagenesis comb jellies important invading species pelagic predators Tissue Grade Biradial Symmetry Marine Convergent with Cnidaria: Clear, jelly-like (jelly plankton) Predatory Simple body plan Different than Cnidaria: No Polymorphism No Sessile Stage Not Colonial Have muscle cells One Way Gut – mouth anus functional? Swim with oral side leading 2 Hermaphroditic Indirect life history larva unlike Cnidaria With or without feeding tentacles Mouth Ctenes – plates of fused cilia Colloblasts - sticky cells catch prey Anus Ctenes - Plates of fused cilia 8 rows = combs Tentacles with colloblasts Construction and Body Forms in Metazoa Construction Metazoa Grades of Construction: Unicellular - Protozoa - specialization of organelles Unicellular Protozoa Cellular Grade - Porifera - specialization of cell types Porifera Tissue Grade - Cnidaria, Ctenophora - cells organized into tissues Diploblastic - two embryonic tissue layers Ectoderm - outside Ectoderm Endoderm - inside Endoderm Organ Grade - Platyhelminthes and most and other phyla other tissues organized into organs Triploblastic - three tissue layers Ectoderm - outside Endoderm - inside Mesoderm - middle Body Cavities Acoelomate - no body cavity Acoelomate e.g., Porifera - cellular grade e.g., Porifera Cnidaria - tissue grade, diploblastic tissue diploblastic Platyhelminthes - organ grade, triplo Platyhelminthes organ triplo Pseudocoelomate - body cavity, but not a true coelom body coelom Triploblastic. Mesoderm on only one side of the the cavity cavity formed from the blastocoel - the cavity the embryonic space in the blastula embryonic e.g., Nematoda, Rotifera, Tardigrada e.g., Nematoda Rotifera Tardigrada 3 Coelomate - true coelom, body cavity lined by Coelomate true coelom body mesoderm (= Peritoneum) on both sides mesoderm Formed by a split in the mesoderm - Schizocoel Or by an out pocketing of the mesoderm - Enterocoel e.g., Annelida, Mollusca, Arthropoda e.g., Annelida Mollusca Arthropoda can have other large sinuses in body e.g., Arthropods have a Haemocoel - blood sinus e.g., which can have functions similar to other cavities Phylum Platyhelminthes Platyhelminthes flatworms Free living or Parasitic Ectoparasitic - Outside Endoparasitic - Inside Bilateral Symmetry Cephalized – Head region concentration of nervous tissue, sensory structures Anterior Posterior Ventral – with mouth Dorsal - opposite mouth Right / Left Triploblastic Organ Grade Dorsal Acoelomate No body cavity organs surrounded by cells - parehchyma (mesoderm) Posterior Mouth Head Anterior Ventral 4 Organ Grade - tissues form organs, specialized for different functions example: Flame cell = Protonephridia Excretory, osmoregulatory organ No circulatory system Must rely on diffusion effective over very short distances Special dorso-ventral muscles keep body flat Protostomes Spiralian Development Müller’s Larva Larva seen in Turbellaria seen Turbellaria Your Text uses 4 classes Your Two classes of flukes: Class Turbellaria - mostly free living, mostly some endo (inside body) and endo and some ecto (outside body) parasites ecto Tegument Ciliated Simple life cycle elaborations of gut and repro systems determine orders from no gut, to extremely elaborate Know taxa: Tricladida Polycladida Rhabdocoela Class Monogenea - single host specific flukes Class Monogenea life cycle – 1 generation, 1 host most ectoparasitic Tegument – nonciliated, syncytium hermaphroditic (or mate for life) Class Trematoda endoparasitic groups Digenea and Aspidogastrea and Aspidogastrea Tegument Complex Life Cycles – Multiple Hosts 5 Class Cestoda – Tapeworms specialized all endoparasitic no mouth, digestive cavity Tegument - syncytial Scolex, proglottids Hermaphroditic Usually vertebrate definitive host; fish, arthropods intermediate hosts For species with multiple hosts: Definitive Host – host for adult Intermediate Host – host(s) for larval stages Class Turbellaria believed to have ancestral characters generally free living simple life cycle mostly predators (eat live animal prey) Most aquatic Mostly marine, some freshwater Terrestrial – Tterrestrial in moist habitats 6 Locomotion: Muscles - circular and longitudinal Dorsoventral - keep flat but not used in locomotion Cilia - glide across surfaces ciliated outer body Bdelloura - obligate commensal with horseshoe crab Polyclad Turbellarian ectoparasite does not feed on the horseshoe crab - just uses it as habitat does See this in lab Observe this in the lab with the live flatworms and in the slide material Do they use both at the same time? When is one more impt. than the other type? Nervous system conc. Anteriorly - has a brain = cerebral ganglia Nerve cords (2), commisures connect cords across body Sensory structures: Light Chemical stimuli Touch 7 ...
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