bio 40 lab 4

• Flatworms

  • Bilaterally symmetrical
  • Dorsoventrally flattened
  • First animal phylum to possess complete organ systems
  • Acoelomate body design
• Mesoderm

  Forms the connective tissue, the parenchyma, which fills the body spaces between the ectoderm and endoderm so that there is no coelom
• Alimentary canal

  Embedded in a solid parenchyma of mesodermal cells and opens through the mouth (no anus)
• Excretory system


  Made of protonephridia, which have osmoregulatory functions
• Flatworms are usually hermaphroditic
• Flatworms have biflagellated sperms
• Flatworms lack circulatory and respiratory systems
• Flatworms

  • Free-living
  • Parasitic
• Most of the approximately 30,000 species of flatworms are parasitic
• Almost all invertebrates (especially molluscs) and vertebrates are host to at least one species of a flatworm
• Most research on flatworms deals with the pathogenic trematodes (e.g. Schistosoma) and cestodes (e.g. Taenia) of humans and their domesticated animals
• Classes of Platyhelminthes

  • Turbellaria
  • Monogenea
  • Trematoda
  • Cestoda
• Class Turbellaria

  • Free-living or commensal; most are marine, but many freshwater types can also be found; epidermis ciliated; specialized adhesive organs; mouth ventrally located
• Class Monogenea

  • Mostly ectoparasitic; usually a single host; development is direct (without distinct larval stages); adhesive organs present both in anterior and posterior regions; with tegument (a natural protective body covering)
• Flatworms

  • Bilaterally symmetrical
  • Dorsoventrally flattened organisms
  • First animal phylum to possess complete organ systems
  • Acoelomate body design
• Mesoderm


  Forms the connective tissue, the parenchyma, which fills the body spaces between the ectoderm and endoderm so that there is no coelom
• Alimentary canal


  Embedded in a solid parenchyma of mesodermal cells and opens through the mouth (no anus)
• Excretory system


  Made of protonephridia, which have osmoregulatory functions
• Flatworms

  • Usually hermaphroditic
  • Sperms are biflagellated
  • Circulatory and respiratory systems are absent
• Flatworms

  Either free-living or parasitic
• Most of the approximately 30,000 species are parasitic
• Almost all invertebrates (especially molluscs) and vertebrates are host to at least one species of a flatworm
• Most research on this group deals with the pathogenic trematodes (e.g. Schistosoma) and cestodes (e.g. Taenia) of humans and their domesticated animals
• Classes of Platyhelminthes

  • Turbellaria
  • Monogenea
  • Trematoda
  • Cestoda
• Class Turbellaria


  • Free-living or commensal
  • Most are marine, but many freshwater types can also be found
  • Epidermis ciliated
  • Specialized adhesive organs
  • Mouth ventrally located
• Class Monogenea


  • Mostly ectoparasitic
  • Usually a single host
  • Development is direct (without distinct larval stages)
  • Adhesive organs present both in anterior and posterior regions
  • With tegument (a natural protective body covering)
• Class Trematoda


  • Flukes (general common name)
  • Ectoparasitic or endoparasitic
  • With tegument
  • With specialized adhesive organs
  • Mouth is anterior and leading into 2-branched intestine
  • Ovary is single and testes usually paired
• Subclass Digenea


  • Mostly endoparasitic
  • Adhesive organs present
  • Their first host is a mollusc and their final host is a vertebrate
  • Members of this group are of medical importance to humans and domestic animals
• Class Cestoda


  • Tapeworms
  • Endoparasitic (usually in the intestines of vertebrates)
  • Adhesive organs on scolex (anterior end of a tapeworm)
  • Body is strobilate (asexual reproduction)
  • With tegument
  • Each segment (proglottid) bears one or to complete hermaphroditic reproductive system
  • No digestive system or sense organs