Download Biology Chapter 27 (Worms and Mollusks)

Worms and Mollusks
Chapter 27
Phylum:Platyhelminthes
(flat) (worm)

Simplest bilateral symmetric animals
showing a head and tail region.
 3 layers: endoderm, ectoderm,
mesoderm
 Known as acoelomates (without a
coelom)
 coelom : a fluid-filled body cavity
General body structure:
Feeding
 Free-living flatworms
 Tiny
can eat:
aquatic animals
 Dead animals
 Single opening to function as a mouth and
anus.
 Possess a pharynx
Respiration, circulation,
excretion
 Breath
through
diffusion
 Flame cells:
specialized cells
used for
removing excess
water.
Planarians (c. Turbellaria)
Free-living
freshwater flatworm.
Possess a digestive tract, mouth,
pharynx, and branched intestine.
Feed on small microscopic animals
No skeletal,circulatory,or
respiratory system
Planarians continued
 Small
brain with
two nerve cords
 Hermaphrodites
 Internal
fertilization
 Can also
reproduce
asexually.
Parasitic flukes (c. Trematoda)

Usually two or
more hosts. (Page
687)
 Primary host:
human (site of
asexual
reproduction)
 Causes the disease
schistosomiasis
Tapeworms (c. Cestoda)

Parasites. Example: beef tapeworm
 Head region (scolex) : contains suckers and
hooks used to attach to a host organism.
 Proglottids : square body segments used for
reproduction
Phylum: Nematoda
(roundworms)
Long cylindrical bodies
Often covered with a thick cuticle
1 mm to 1 meter in length
Both free-living and parasitic
*** 2 body openings***
Major difference from the flatworms
Food and wastes will NOT be mixed
Form and function





Eat small animals, bacteria, algae,
fungi, etc
Exchange gases through diffusion
Possess a simple nervous system
Move through contracting muscles
Reproduce sexually
Trichina worm

Causes trichinosis
 Often present in pigs. Grow to about one
millimeter in length and become cysts in pig
muscles.
 People eat contaminated pork and larval
cysts develop into adults in human
intestines.
 New larvae can end up in human muscles.
Ways to prevent trichinosis:
1.
2.
3.
Thoroughly cook pork products
Feed hogs uncontaminated feed
Freeze pork immediately after packaging
Filaria

Roundworm that
causes the disease
elephantiasis.
 Carried by mosquitoes
 Infects bloodstream
and blocks lymph
nodes resulting in
severe swelling.
Ascarid worms
 Affects
more
than 1 billion
people
 Affect people,
horses, pigs,
chicken, cattle,
dogs, cats etc.
Pinworms and Hookworms

PINWORMS
 Most common nematode infection in N.
America
 Especially infants and toddlers.
HOOKWORMS
 Often
will enter
through the feet.
 Common in areas
where sewage
disposal is
inadequate
Phylum: Annelida

Also known as the segmented worms.
 The body is divided into separate body
segments.
 Marine,fresh water,and on land.
 Parasitic and free-living. ex.
…more annelid facts
“tube within a tube” body plan.
 Closed circulatory system, 2 openings

respiration

Aquatic annelids breathe using gills
 Land-dwelling annelids breathe through the
skin
excretion
Nephridia
: excretory organs
that filter nitrogenous waste in
the ceolom.
Reproduction

Hermaphroditic. eggs and sperm released at
the clitellum
 C.
Oligochaeta
 First segment = prostomium
 Setae = small hair-like extensions
on ventral surface used for
locomotion.
 Possess many “hearts”
The “hearts” of an earthworm:
Ecology of Earthworms
Help to aerate the soil
2) Provide nutrients in to the soil in
fecal matter
3) Participate in a wide range of
food chains
1)
 Mainly
freshwater.
 Suckers on both ends of body
 Saliva of leeches contain enzymes
that prevent blood from clotting
(anticoagulants)
Leech Anatomy
 Attaches
to prey with posterior sucker,
and uses anterior sucker to “suck”
blood.
Medicinal uses of leeches
 Used
to be used for “leeching” by early
physicians to rid a sick person of “bad”
blood.
 Still used in surgery to prevent blood
clotting and unwanted swelling due to
excess blood.
Phylum: Mollusca

Second largest phyla of animals after the
arthropods.
 Found in fresh water, salt water, and on land
 ex.
Mollusk characteristics:

Soft bodies, 3 cell tissue layers
 Many are used for food and jewelry
 Possess a foot = large ventral muscle used
for movement.
 Most have a radula (exception: bivalves)
 Mantle - fold of skin that surrounds the
body organs
1. bivalves

2 parts to their shells.
 Strong adductor muscles to keep the shell
closed
 Incurrent siphon – carries water and food
into the mantle cavity
 Excurrent siphon – siphon where water is
expelled.
Examples of bivalves:
pearls

Mother-of-pearl inner
smooth part of bivlave
shell.
 Made primarily by
oysters when a foreign
object gets lodged
inside between mantle
and shell.
 Come in many colors
Reproduction and nutrition
 Bivalves
are filter-feeders. (plankton
and small invertebrates)
 Separate sexes
 Sperm is released by the excurrent
siphon and enters a female via the
incurrent siphon where fertilization
takes place.
2. gastropods

Largest class of mollusks
 Most possess a single shell.exception: slug
3. cephalopods

Most advanced mollusks
 All are marine predators
 Use tentacles to gather and manipulate food
 Can swim rapidly by expelling a jet of
water from their mantle cavity.
 Some may discharge an inky fluid for
defense
 Octopus (8 arms) squid (10 tentacles)
examples: