Unsegmented Worms
Flatworms
Flatworms
• Belong to the phylum platyhelminthes.
(Plat = flat)
• There are three classes:
– Turbellaria
– Trematoda
– Cestoda
Characteristics of Flatworms
• They are acoelomates (they don’t have body
cavities)
• They have bilateral symmetry
• Show cephalization
• Respiration through skin
• Single opening to digestive tract (pharynx)
Class Turbellaria
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Spade-shaped head and two eyespots
Eat protozoans for scavenge
Flame cells remove waste
Are hermaphrodites (have male and
female reproductive parts)
• Can reproduce by regeneration
• Are free-living
Class Trematoda
• Are parasitic
flukes
• Have suckers on
both ends of the
body
• Can live inside or
outside of host
Class Trematoda
• Nervous and excretory
systems like
turbellarians
• Hermaphrodites
• Have complex life
cycles
Fluke Life-Cycles
The long and complex life-cycle of the fluke can
be made easier to
understand through the use of a nonsense
mnemonic :
Every - Egg
Mirror - Miracidium (free-living in water)
Spotted - Sporocyst (in snail)
Red - Redia (in snail)
Certainly - Cercaria (free-living in water/snail)
Met - Metacercaria (in 2nd intermediate host)
Approval - Adult
Class Cestoda
• Parasitic
• Tapeworms
• Long, ribbon-like
bodies
• Absorbs
nutrients from
host
• Hermaphrodites
Tapeworm
Anatomy
Roundworms
Roundworms
Roundworms
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Belong to phylum Nematoda
Pseudocoelomates (fluid filled body cavity)
Slender bodies that taper on both ends
Have mouth and anus
Can be free-living or parasitic
Pinworms live
in human
intestines
Trichinosisa disease
from eating
infected
pork
Cysts in Contaminated Pork
Rotifers
• Known as rotifers or wheel
animals
• Transparent, free-swimming
microscopic animal
• Freshwater & marine
• Have a ring of cilia around
mouth that rotates like a wheel
to bring in food
• Feed on unicellular algae,
bacteria, & protozoa
Rotifers
• Have a muscular organ
called the mastax behind
the pharynx to chop food
• Nervous system
composed of anterior
ganglia & 2 long nerve
cords
• Show cephalization (head
end)
• Have 2 anterior, lightsensitive eyespots
Rotifer Anatomy