This document provides information about flatworms (phylum Platyhelminthes), including their defining characteristics, habitat, organ systems, and examples of classes. It focuses on three classes: Turbellaria which are mostly free-living freshwater forms, Trematoda which are mostly parasitic with a leaf-like flattened body and attachment structures, and Cestoda which are exclusively parasitic tapeworms lacking digestive systems. Specific examples covered are the liver fluke Fasciola hepatica and the tapeworms Taenia saginata and T. solium, including details of their life cycles and pathogenesis.

1. BIOL 105
https://www.youtube.com/watch?v=guQOYTkYof8
https://www.youtube.com/watch?v=m12xsf5g3Bo

2.  (Platys: flat; helminthes: worms)
 Habitat: mostly live as parasites, few are free
living in sea water or fresh water
 Grade of organization: Organ- system grade
of organization
 Symmetry: Bilateral symmetry and Body is
dorso-ventrally flattened

3.  Germ layer: Triploblastic. Ectoderm is very
specialized with distinct epidermis for living
inside the host
 Digestive system: incomplete or absent in
parasitic forms in particular, simple one
present in free living forms
 No mouth (oral opening directly into pharynx)
 No true stomach structure (pharynx opens
into a complex “intestinal” structure)
 In tapeworms, Direct absorption of soluble
nutrients by cells and tissues

4.  Excretory system: Protonephridia (old kind of
nephridia) having flame cell inside
 Respiration: by simple diffusion of gases
through body surface
 Circulatory system: Absent
 Reproduction
 Sexual: by gamatic fusion, hermaphrodite
 Asexual : by regeneration and fission
 Fertilization: internal
 Life cycle is complex involving one or more
hosts

5.  Class 1 Turbellaria
 § Mostly Free-living fresh water organism,
dorsoventrally flattened body, no hooks or
suckers
 § E.g., Planaria, Bipalium, Otoplana,
Notoplana
 Class 2 Trematoda
 § Mostly parasitic, dorsoventrally flattened
body (leaf like), have hooks and suckers
 § E.g. Fasciola hepatica (Liverfluke), Blood
fluke

6.  Class 3 Cestoda
 § Exclusive parasitic, dorsoventrally flattened
body (tape like), hooks and suckers, digestive
system absent, protonephridia present
 § E.g. Taenia spp ( tapeworm),

7. The Sucker

8.  . It is commonly known as “Liver fluke” and is an
endoparasite in the bile duct of sheep’s liver.
 It is cosmopolitan and pathogenic and measures
about 20 to 50 mm in length and 5 to 15 mm in
width.
 Body dorsoventrally flattened and leaf-like.
 Anteriorly, the mouth and oral sucker are
situated on a small protuberance-the “head”.
 A little behind the oral sucker lies a ventral
sucker or acetabulum in the median line on
ventral side.

9.  Among the digestive organs the most
conspicuous is intestine, which is a highly
branched and convoluted structure.
 In between the oral and ventral suckers is
present a small genital opening along the
ventral surface.
 In the posterior part lies a sub-terminal
excretory pore or “anus”.

10.  They are hermaphrodite and the reproductive
organs occupy almost whole of the body
space.
 The life cycle includes an intermediate host in
the form of snail Limnea (a mollusc).
 It causes liver rot, liver cirrhosis, eosinophilia
and anemia.

12. The cestodes (tapeworms) Taenia saginata (beef tapeworm) and T.
solium (pork tapeworm). Taenia solium eggs can also cause cysticercosis.

13. Life Cycle of Tape worm with two hosts
(https://projects.ncsu.edu/cals/course/zo150/mozley/fall/studyaids.html)