Platyhelmenthis

• Classification


  The science of identifying and naming species, and arranging them into a classification
• Taxonomy


  Organisms are arranged in a hierarchical structure using taxonomic categories or groups
• Binomial nomenclature


  Two-name system developed by Swedish biologist Carolus Linnaeus in 1758 and used today
• Animal classification criteria


  • Physical characteristics
  • Animal Systematics: Evolutionary relationships of organisms
• Physical characteristics


  • Number of germ layers (diploblastic or triploblastic)
  • Body Cavity
  • Nature of digestive system (one opening or two openings)
  • Body segmentation
  • Body symmetry
  • Type of skeleton
  • Nature of skeleton
  • Number and arrangement of appendages
• Most taxonomists today believe that classification systems should reflect the evolutionary relationships of organisms
• Significance of animal classification

  • Assign specific names
  • Establish the relationship among different organisms and to know about their evolution
  • Serve as an aid to memory
  • Enhance communication, as scientific names assigned are used globally irrespective of language
• Platyhelminthes


  Flatworms: simplest animals
• Characteristics of Platyhelminthes


  • Dorso-ventrally flattened
  • Size range from a millimeter to many meters in length
  • Bilateral symmetry
  • Triploblastic
  • No internal body space (acoelomates)
  • Organs embedded in parenchyma (specialised connective tissue)

  
• Digestive system of Platyhelminthes


  • The smallest free-living forms lack digestive system
  • Digestive tract has a single opening - the mouth/anus
  • Some possess a digestive system, with branching intestine from which the nutrients are absorbed
• Class Turbellaria


  Mostly free-living flatworms with ciliated epidermis
• Habitat of Turbellaria


  • Marine
  • Fresh-water
  • Terrestrial (moist soil especially in temperate climate)
• Characteristics of Turbellaria


  • Mostly creeping worms varying in size
  • Locomotion: muscular and ciliary movement
  • Voracious carnivores, eating any small animals, usually worms and crustaceans
• Turbellarians are triploblastic
• Anatomy of Turbellaria


  • Triangular head has two ocelli (eyespots)
  • Two auricles (earlike projections) which are sensitive to touch and the presence of certain chemicals
• Feeding and Digestion in Turbellaria

  1. Detect food by chemoreceptors

  2. Wrap themselves around prey

  3. Small prey are taken into the gut and surrounded with digestive enzymes

  4. Fats directly broken down into soluble foods (extracellular digestion)

  5. Proteins and carbohydrates are absorbed by the cells lining the gut and digested there (intracellular digestion)
• Respiration and Excretion in Turbellaria

  • No respiratory organs, exchange of gases occur through body surface
  • Flame cells remove the unwanted liquids by passing them through ducts that lead to the excretory pores
• Asexual Reproduction in Planaria

  1. The planarian detaches its tail end, and each half regrows the lost parts by regeneration (pluripotent cells called neoblast)

  2. Can posses two heads or tails if not completely detached
• Sexual Reproduction in Planaria

  1. Turbellarians are monoecious (hermaphroditic) but practice cross-fertilization

  2. Some species practice "penis fencing": Pairs compete to transfer sperm to the other

  3. After copulation, fertilized eggs & yolk cells become enclosed in cocoon, embryos emerge as juveniles
• Trematodes (flukes) are estimated to include 18,000 to 24,000 species
• Characteristics of Trematodes


  • Flattened, leaf-like bodies (few mm to 8 cm long)
  • Unsegmented
  • Nearly all are parasitic, either internal or external parasites
• Two major groups of Trematodes

  • Blood flukes
  • Tissue flukes
• Blood flukes


  • Schistosoma mansoni
  • S. japonicum
  • S. hematobium
• Tissue flukes


  • Fasciolopsis hepatica, F.buski
  • Clonorchis sinensis, Opistorchis
  • Paragonimus westermani
• Classification of trematodes


  • Blood flukes
  • Tissue flukes
• Trematodes (flukes)


  • Estimated to include 18,000 to 24,000 species
  • Flattened, leaf-like bodies (few mm to 8 cm long)
  • Unsegmented
• Trematodes


  • Nearly all are parasitic
  • Either internal or external parasites
• Trematodes


  • One or two suckers (oral ventral suckers) for attachment and feeding
  • Outer tegument armed with tiny spines for attachment
  • Inhabit a variety of sites in their hosts: digestive tract, respiratory tract, circulatory system, urinary tract and reproductive tract
• Trematodes


  • Well-developed alimentary canal, but incomplete, no anus
  • No coelom/ body cavity
  • No blood vessels, simple ladder nervous system
• Oviparous


  Lay eggs
• Operculated eggs


  Exception is schistosome eggs
• Hermaphroditic


  Except blood flukes
• Generalized life cycle of flukes

  1. Definitive host: Man

  2. Intermediate host: fresh water snail, fish, crab

  3. Some trematodes have 2 or 3 intermediate hosts before the definitive host is reached
• Hermaphroditic flukes


  Both male and female
• Metacercaria

  Infective for humans
• Bisexual flukes


  Separate sexes
• Cercariae


  Infective for humans
• Life cycle of intestinal fluke: Fasciola spp


  Maturation from metacercariae into adult flukes approx. 3-4 months in humans
• Fasciola hepatica (sheep liver fluke)


  • May be asymptomatic
  • Symptoms include coughing and vomiting, generalized abdominal rigidity, headache and sweating, irregular fever, diarrhea and anaemia
  • Infects various mammals, including humans
• Blood flukes or schistosomes


  • Only bisexual flukes that infect humans
  • General body structure same as that of hermaphroditic flukes
  • Both sexes live in lumen of blood vessels (in close association)
  • Male worm broader & heavier with large ventral groove (gynaecophoral canal)
  • Female lies within a tegumental fold, gynaecophoral canal