Notes for this class of Platyhelminthes

1. Phylum: Platyhelminthes
Class: Trematoda
Flukes

2. Flukes, like tapeworms, are
parasites of vertebrate
animals. The anterior end of
this one is at the top of the
photograph.
The black “squiggly” lines are
excretory ducts that collect
wastes from cells and excrete
them. The dark bow-shaped
lines that extend from anterior
to posterior, are longitudinal
nerves.
Flukes are round to football-
shaped, but the head is
always a bit pointed.

3. 1
2
3
1 Ganglion – it is the flatworm’s primitive brain and is formed by the
fusion of the two longitudinal nerves.
2 Longitudinal nerves extend the length of the flatworm’s body on
both sides.
3 Transverse nerves branch towards the ectoderm from the
transverse nerve.

4. Fluke life cycles are complex and
usually involve two hosts, one is
for the adult fluke (in this diagram
a cow or sheep) and is called the
definitive or primary host. The
intermediate host is infested by
the fluke’s larvae (a snail in the
case of the sheep liver fluke).
Liver flukes live and reproduce in
the bile duct (duct from gall
bladder to liver). Notice that there
are two larval stages (the
miracidium and the cercariae).
This fluke evolved with sheep and
snails. All flukes have similarly
complex life cycles that include
two larval forms and multiple
hosts.

5. The Chinese liver fluke is a
human parasite. Its
intermediate hosts include
snails and fish.
Humans become infected by
eating raw or poorly cooked
fish.
In some fishing villages in
southeast Asia, medical tests
have proven that 100% of the
human residents are infested
because the people’s diet
includes raw fish.
In such villages, human feces
are often dumped into the
same waters that fishes are
taken from as a food source.

6. The End