PLATYHELMINTHES
PLATYS
FLAT
HELMINTHES
WORMS
General Characteristics
Free-living or parasitic
The simplest animals that are bilaterally
symmetrical,
First animals with 3 germ layers -
triploblastic
◦ Ectodermis
◦ Mesodermis
◦ Endodermis
Epidermis has cilia or cuticle
Coelom lacking (acoelomate).
The phylum Platyhelminthes represents all
flatworms in the kingdom Animalia.
CLASSE
S
Class Turbellaria - Free Living Worms
Class Trematoda - Flukes
Class Monogenea - Flukes
Class Cestoidea - Tapeworms
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.
Turbellarians have no cuticle (external layer
of organic but non cellular material).
In a few species, the skin is a
syncytium, 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.
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 detritus.
On the anterior end (head) are eyes.
The anterior end possesses lateral
projections called auricles.
Phylum Platyhelminthes
8
•
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.
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.
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
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.
Parasites ???
Class Trematoda
Live as endoparaeyte/ endoparacyte.
Size is less than 1mm to more than 8cm.
Oval or elongate shaped
Digestive system, nervous system redused
compared to Turbellaria.
(e.g., Fascioloaris, Clonorchis)
Reproduction
Class Monogenea
Free-living flatworms are predators.
Live in water or in shaded ,humid
terrestrial environment such as leaf
litter.
Ciliated larvae.
Most
distinguishing
feature is the
presence of a large
attachment organ
called an
opistohaptor
Have a single host.
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.
Hooks can withdraw or extend.
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.
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.
•
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
BODY CAVITY
Acoelomates
SYMMETRY
Bilaterally symmetrical
Dorsoventrally flattened
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, is a
blind system.
NERVOUS SYSTEM
Anterior cerebral ganglia, longitudinal
nerve cords, nerve cords, and some
lateral nerve
Sensory organs
( e.g. Eye spots, statocytes )
Reproduction
Platyhelminthes reproduction
occurring types
Asexual reproduction Sexual
reproduction
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
Combinations of flame cells and tube cells
are called protonephredia.
Distinguished feature of phylum
Platyhelminthes
Flame cells.
Diseases cause by
Platyhelminthes for fish
Intense monogenean infections induce
respiratory and osmoregulation dysfunctions.
Metacarcarial infection
It may affect the growth and survival or
disfigure fish so they lose their market value
as a food or ornamental profucts.
Cestodiasis
Low number of pleurocercoides may be
located in vital organs such as the brain,
heart, spleen, kidney or gonad and have a
devastating affects on the fish.
Presence or absence of cilia
Free living adult have cilia
Larval stage of parasitic animals have
cilia