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[7] Platyhelminthes.docx

Course Code
BIOL 2030
Scott Kelly

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Platyhelminthesflatworms, flukes, tw
Bilateral Symmetry
Having two sides symmetrical about one median axis only, so that one side is a mirror
image of the other
Any member of the order Tricladida, free-living flatworms (platyhelminths) living in
streams, ponds, lakes, and the sea. They have a broad, flattened body, well-
developed sense organs at the anterior end, and an intestine with three main
Short, rod-like body in epidermal cell of turbellarians, which is discharged if the worm
is injured and swells up to form a gelatinous covering
Viscid Cells
Sticky cells
Anchor Cells
Attachment cells
Releasing Cell (Gland)
Secreting cell
Pedal Wave
“foot wave” – means of free-living flatworm movement
Branching excretory duct of the protonephridial system ( excretory system in some
simple invertebrates such as flatworms, nematodes, annelids, and rotifers. It consists
of a system of branching ducts (protonephridia) each enclosed at its internal end by a
flame cell, and opening into a central duct or to the surface through pores. Flame
cells beat a large bundle of flagella which project into the duct, and whose motion
gives a flickering appearance under the light microscope similar to a flame
Cerebral Ganglion
The supraoesophagal gangla, or “brain” of invertebrates
Chain of proglottids of tapeworms
Region at anterior end of tapeworm containing minute hooks and a sucker, by which
it attaches itself to the gut wall
Individual segment of an adult tapeworm, containing a set of reproductive organs.
Eggs are formed in the posterior proglottids, and are shed in the feces and then enter
the alternative host where they hatch
Spherical, hooked larva that hatches from tapeworm egg and develops into a
Intermediate host
Organism in which a parasite lives for part of its life-cycle but in which it does not
become sexually mature
Definitive Host
Host of an adult parasite
Ciliated larval stage of gut, liver, and blood flukes, which hatches out of the egg and
infects the snail host
One of the larval stages in the life-cycle of endoparasitic flukes, which develops from
the miracidium in the snail host. I thas no mouth or gut and reproduces asexually to
produce rediae or cercariae
A larval stage of some endoparasitic flukes in the snail host. I tis produced asexually
from the sporocyst, has a mouth and gut and reproduces asexually to produce a
further generation of rediae or cercariae
Heart-shaped, tailed, larval stage of a trematode (fluke) produced in the snail host. It
is released from the snail, sometimes then encysting, and subsequentily infects a
vertebrate host

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The stage in the life-cycle of endoparasitic flukes that develops from a cercaria, in
which the cercaria loses its tail. In schistosomes this occurs after infection of the
vertebrate host by cercariae. In other species metacercariae infect the vertebrate
host. The adult parasite develops directly from a metacercaria
Posterior adhesive organ in trematodes
Anterior adhesive organ in trematodes
Overview of Body Plans
Platyhelmonthes characterized by bilateral symmetry
Ventral side used for locomotion
Cross-Section of planarian:
red -> circular muscle, for elongation/shortening of
Rhabdites locomotion lubricant (see defins)
Body Structure & Locomotion
Ciliated Ventral
Subtle muscular contraction
Dual-Gland adhesive organs
o Paired viscid cells glands prod. Adhesive secrections attach anchor cells to substratum
o Anchor cells bear strain of attachment, & allow subtle muscular contractions to pull
animal forward (muscular contraction = pedal wave)
o Releasing cell gland prod. Chemicals that release anchor cell attachment
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