WORMS AND MOLLUSKS
Biology 112
FLATWORMS
 Phylum Platyhelminthes
 Soft, flattened worms
with tissues and internal
organ systems
 The simplest animals
with three germ layers,
bilateral symmetry and
cephalization
 Acoelomates
 A coelom is a fluid-filled
body cavity that is lined
with tissue in the
mesoderm
 No coelom between the
tissues of flatworms
BODY FUNCTIONS OF FLATWORMS
All use diffusion for distribution of
nutrients and gases
Some have specialized flame cells used
to remove excess water from the body
Contain a digestive cavity with one
opening – a mouth
A muscular tube, called a pharnyx,
pumps food into the digestive cavity
CLASSIFICATION OF FLATWORMS
1.
Tubellarians
-
Free-living flatworms,
can live in fresh and
salt water
Ganglia control the
nervous system
Some contain an
eyespot to detect light
Reproduce asexually
and sexually
Planarians are the
most familiar species
CLASSIFICATION OF FLATWORMS
2. Flukes
- Parasitic
- Infect the internal
organs of their host
- Reproduce sexually
in the primary host
and asexually in the
intermediate host
CLASSIFICATION OF FLATWORMS
3. Tapeworms
- long, flat parasitic
flatworms
- Live in the intestines
of their hosts
ROUNDWORMS
Phylum
Nematoda
Unsegmented
worms that have
pseudocoeloms
Also have a
digestive system
with a mouth and
an anus
ROUNDWORMS AND BODY FUNCTIONS
Rely on diffusion for respiration,
circulation and excretion
Muscles and fluid in the
pseudocoelom act as a hydrostatic
skeleton
Reproduce sexually by internal
fertilization
CHARACTERISTICS OF ROUNDWORMS
Most are free-living
but some are
parasitic
Parasitic include:
 Trichinosis-causing
worms
 Hookworms
ANNELIDS
 Phylum Annelida
 Earthworms
 Segmented bodies
 Have a true coelom that is lined with tissue from the
mesoderm
 Internal walls called septa separate the segments
that divide the body
 Most segments are similar to one another
 A few are specialized with eyes or antennae
 Many have bristles called setae attached to each
segment
INTERNAL STRUCTURE OF ANNELIDS
Complex organ structures
Many contain a pharynx that is used to get
their food
Food moves through the crop, where it is
stored
Then moves to the gizzard, an organ that
grinds it into smaller pieces
EARTHWORMS
 Class Oligochaeta
 Hermaphroditic
 Has both male and
female reproductive
organs
 When eggs are ready to
be fertilized, a clitellum,
a band of thickened
segments, secretes a
mucous ring in which
fertilization takes place
 Streamlined body with
few setae
 Can live in fresh water or
soil
MOLLUSKS
Phylum Mollusca
Soft-bodied animals that often have
an internal or external shell
Can be herbivores, carnivores,
detritophores or parasites
BODY PARTS OF A MOLLUSK
 Foot
 Used for crawling,
burrowing and capturing
prey
 Mantle
 A thin layer of tissue that
covers most of the body
 Visceral mass
 Makes up the internal
organs
 Shell
 Glands secrete calcium
carbonate
CLASSIFICATION OF MOLLUSKS
Gastropods
 Includes pond snails
and land slugs
 Single-shelled or shellless
 Move by using a
muscular foot on their
left ventral side
 Use a flexible tongue
called a radula to eat
CLASSIFICATION OF MOLLUSKS
Bivalves
Clams, oysters,
mussels and
scallops
Two-shells held
together by muscles
CLASSIFICATION OF MOLLUSKS
Cephalopods
 Includes octopus and
squid
 Soft-bodied mollusks in
which the head is
attached to a single foot
 Foot is divided into
tentacles
 Small internal shells or
no shell at all
 Have complex sense
organs