PLATYHELMINTHES.

1. PLATYHELMINTHES

2. PLATYHELMINTHES

3. PLATYS HELMINTHES
FLAT WORMS

4. General Characteristics
⚫ Free-living or parasitic
⚫ The simplest animals that are bilaterally symmetrical,
⚫ First animals with 3 germ layers -
• triploblastic
◦ Ectodermis
◦ Mesodermis
◦ Endodermis

5. ⚫Epidermis has cilia or cuticle
⚫Coelom lacking (acoelomate).
⚫The phylum Platyhelminthes represents all
flatworms in the kingdom Animalia.

6. CLASSES
⚫Class Turbellaria - Free Living Worms
⚫Class Trematoda - Flukes
⚫Class Cestoidea - Tapeworms

7. Turbellaria
⚫(e.g., Planaria)
⚫They are mostly free-living, and range from 1
mm (0.039 in) to 600 mm (24 in) in length.
⚫Most are predators or scavengers, and
terrestrial species are mostly nocturnal and
live in shaded, humid locations, such as leaf
litter or rotting wood.

8. ⚫Turbellarians have no cuticle.
⚫ In a few species, the skin is a collection of
cells with multiple nuclei and a single,
shared, external membrane. However, the
skins of most species consist of a single
layer of cells.
⚫Non parasitic animals.

9. ⚫ Some species also have a protrusible pharynx that
captures food and transfers it into the mouth
⚫ Can be carnivores or scavenge on dead animals
and debris.
⚫ On the anterior end (head) are eyes.
⚫ The anterior end possesses lateral
projections called auricles.
⚫ A ciliated epidermal layer covers the body.

10. • Loosely connected mesenchyme cells
surrounds the gut.
• Locomotion
• Swim or crawl by cilliary population.
• Feeding & Digestion
• Mouth is an opening located on the mid
ventral line.
• Food goes through this mouth and pharynx
like tube into gastro vascular cavity.

12. ⚫When the animal is feeding pharanyx is
projected out of the mouth.
⚫There is no anus, so undigested food
particles are ejected through mouth.
⚫Excretion
⚫Consists of an interconnecting series of
excretory canals.

14. ⚫Cillia containing flame cells are found at the
end of the side branches of these canals.
⚫These flame cells are most important for
water balance.
⚫Reproduction
⚫Asexually – Transverse fission
⚫Sexually – Copulation

15. ⚫Nervous system
⚫Two longitudinal nerves that extend the
length of each side of the body.
⚫It forms a brain in the anterior region.
⚫Series of transverse nervous can be seen.

16. Class Trematoda
⚫Live as endoparasite.
⚫Size is less than 1mm to more than 8cm.
⚫Oval or elongate shaped
⚫Digestive system, nervous system redused
compared to Turbellaria.

19. Class Cestoda
⚫Endoparasites (E.g. Tapeworms)
⚫The anterior end has scolex. It used
to attach to the hosts body.
⚫Near scolex there is rostrellum that
contains hooks, scolex also include
suckers.

21. ⚫From strobila makes up body. Strobila is a
collection of proglottids.
⚫Most are adapted to live inside the gut of the
host.
⚫4ft to 10ft ( Sometimes 40 feets)
⚫Body is covered by protective cuticle.
⚫Digestive system absent
⚫Reproduction They are hermaphroditic.

22. Body plan
⚫Outer Body Covering
• The body of some Platyhelminthes (e.g.,
turbellarians ) is covered by a ciliated epidermis
• Epidermal cells contain rod-shaped structures
called rhabdites that when released into the
surrounding water, expand and form a protective
mucous coat around the animal.

23. • The outer body covering of other
platyhelminthes (e.g., parasitic forms) is a non-
ciliated tegument
• The tegument is referred to as a
syncytial epithelium

24. Digestive System
• Some of the Platyhelminthes possess a
digestive system, with a mouth, pharynx, and
a branching intestine from which the nutrients
are absorbed
• The intestine, with only one opening.

26. NERVOUS SYSTEM
⚫Anterior cerebral ganglia, longitudinal
nerve cords, nerve cords, and some
lateral nerve
⚫Sensory organs
• ( e.g. Eye spots, statocytes )

27. Reproduction
⚫Platyhelminthes reproduction occurring
types
• Asexual reproduction
Sexual reproduction

28. Excretory System
⚫Flame cells, the beating of their flagella
extract water that contains wastes and some
reusable material, and drive it into networks of
tube cells which are lined with flagella and
microvilli.
⚫The tube cells flagella drive the water towards
exits called nephridiopores