1 / 96

Phylum Platyhelminthes (flatworms)

Phylum Platyhelminthes (flatworms). A phylogeny of Animalia. Platyhelminthes. Bilateria. Phylum Platyhelminthes. The Flatworms Part 1: Free-living Flatworms. Emerging Patterns in Evolution. Bilateral symmetry Dorsal & ventral, anterior & posterior

Download Presentation

Phylum Platyhelminthes (flatworms)

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Phylum Platyhelminthes (flatworms)

  2. A phylogeny of Animalia Platyhelminthes Bilateria

  3. Phylum Platyhelminthes The Flatworms Part 1: Free-living Flatworms

  4. Emerging Patterns in Evolution • Bilateral symmetry • Dorsal & ventral, anterior & posterior • Associated with locomotion on a solid surface • Evolution of a head end: cephalization • Possess a head (leading end with sense organs) • Internal fertilization

  5. Bauplan • Dorsoventrally flattened • Lack circulatory system for transport‑ must rely on diffusion for gas exchange • Triploblastic • Embryo has 3 cell layers • Ectoderm (cnidarians) • Endoderm (cnidarians) • AND NOW, introducing THEMESODERM! • Acoelomate - Hey, where’s my cavity?

  6. Phylum Platyhelminthes – tissue organization • Triploblastic = 3 tissue layers • Ectoderm (outer)Endoderm (inner)Mesoderm (between)

  7. Muscles and Movement Hydrostatic Skeleton

  8. Bauplan • Nervous system • Anterior brain • Paired ganglia and nerves • Pairedventral nerve cords • Longitudinal • Lateral • Incomplete gut • No anus • Food exits via mouth

  9. Phylum Platyhelminthes - digestive system • Gastrovascular cavity • Protrusible pharynx in some taxa • Digestion is both intracellular and extracellular

  10. Bauplan • Excretory system & osmoregulation • Diffusion across body wall • Protonephridia • Specialized excretory organs • Probably mainly for water balance - produces urine- a filtrate of extracellular fluid • May also help osmoregulate

  11. Phylum Platyhelminthes- excretory system • “Protonephridial” system: blind‑ending tubes with flame cells & fenestrae at ends, connected with excretory pores • Probably mainly for water balance produces urine- a filtrate ofextracellular fluid • Flatworms have extracellular fluid compartmentcells protected from external environment • Cnidaria lack this- cells are in contact with water (in freshwater cnidaria, each cell has prominent contractile vacuoles)

  12. Protonephridial osmoregulatory/excretory system “flame cell” fenestrae duct

  13. Bauplan • Lack cuticle or other rigid skeletal support • Lack fluid-filled body cavity • Spermatozoa possess a pair of flagella that arise from the paired centrioles • Epidermal cells are typically multiciliated. • Neoblasts---stem cells that give rise to the other cell types in the body.

  14. endoderm

  15. Life History • Most are simultaneous hermaphrodites • Function as male and female simultaneously • Transfer sperm and receive sperm simultaneously • Monoecious • Most are not self-fertile • (A few exceptions) • Most are oviparous (= produce shelled eggs that are released and hatch outside the body). • Most can also reproduce asexually by budding or transverse fission

  16. Asexual reproduction by transverse fission (budding) • Interesting in 2 ways: • Another flatworm class (cestoda) is segmented ‑ they grow by serial reproduction of body parts • If you cut a turbellarian in half, it can regenerate • Regeneration involves undifferentiated cells in mesoderm called neoblasts

  17. Class Cestoda(tapeworms) all parasitic Class Monogenea(monogenetic trematodes, gill flukes) all parasitic Class Trematoda(digenetic trematodes, flukes) all parasitic Class Turbellaria(turbellarians)mostly free-living Platyhelminthes- 4 classes traditional

  18. Platyhelminthes • Inability of flatworms to synthesize fatty acids and sterols may explain their need for establishing symbiotic relationships • The parasitic classes of flatworms are linked by a synapomorphy- the tegument(see next slide) • Clade Neodermata

  19. Turbellaria “Neodermata” The parasitic flatworms) (Tegument)

  20. Classification • Phylum Platyhelminthes • Classes • Acoelomorpha: • Acoels (free-living) + Neodermata (parasites) • Turbellaria: free-living flatworms • Trematoda: flukes • All are parasites • Cestoda: tapeworms • All are parasites • Monogenea? (Maybe belong with cestoda) • Ectoparasites of fish

  21. Turbellarians were traditionally classified based on the form of the gastrovascular cavity

  22. Acoels are not Platyhelminthes??? • rRNA analysis (see cladograms) shows that Acoela is basal to other bilateral clades • Digestive syncytium instead of a gut • Netlike nervous system, lack brain • Kinked cilia • Acoel eggs cleave only once and the two resulting cells immediately generate many small cells. • Link to more info on Acoela: http://devbio.umesci.maine.edu/styler/globalworming/

  23. 18S rDNA-based maximum-likelihood tree of 61 metazoan species From:Ruiz-Trillo et al. (1999) Acoel flatworms: earliest extant bilaterian metazoans, not members of Platyhelminthes. Science 283:1919-1923 Platyhelminthes

  24. Class Turbellaria • Order Acoela • Small flatworms with no permanent gut cavity. • Free-living, marine and brackish water.

  25. Rhabodocoel turbellarians • Diverse and important predators on meiofauna in freshwater ecosystems • Recent research on predation on freshwater bivalves

  26. Mesostoma – a viviparous rhabdocoel – note the embryos within the uterus

  27. C. Barnhart Mesostoma – close-up showing the babies Mom’s oral sucker Babies Mom’s eyes

  28. Macrostomum – predator on juvenile bivalves

  29. Eggs of Macrostomum

  30. Platyhelminthes • Turbellaria • Tricladida Bipalium A land planarian common in greenhouses world-wide – causing problems in Britain

  31. Bipalium feeding on an earthworm

  32. Class Turbellaria • Order Tricladida • Gut with three branches • Free living • Freshwater • Planarians such as Dugesia • A few inhabit terrestrial (moist) habitats • Neodermata • Exclusively parasitic

  33. Class Turbellaria • Marine species (beautiful colors) • Significant members of coral reef ecosystems • Some are major predators of colonial ascidians (sea squirts) • Others are pests of commercial clams and oysters • Some live symbiotically with/on a variety of reef invertebrates

  34. Bdelloura- a marine triclad that is commensal with horseshoe crabs (most turbellarians are not parasites)

  35. Class Turbellaria • Locomotion • Usually by cilia on a layer of mucus • Dugesia can move at about 1.5 mm/sec • Peristaltic waves can achieve higher velocities • Marine flatworms can use this to swim gracefully • Also use cilia same way as protists do

  36. Rhabdites secrete mucus

  37. Class Turbellaria • Locomotion • Terrestrial planarians • Glide smoothly on the substrate by the action of powerful, closely spaced cilia in a special medial ventral strip (creeping sole), on a thin coat of mucus secreted on the substrate by glands opening into the creeping sole • Planarians that migrate on plants or objects above the ground sometimes lower themselves to the ground on a string of mucus.

  38. Class Turbellaria • Body construction • Lab notes • Live Dugesia • Slides of whole planaria and cross sections

More Related