Ch 27- Worm and Mollusks
• biology: the science of life: world of animals |
Discovery Education
• Phylum Platyhelminthes
• Characteristics of flatworms
– Soft, flattened worms with tissues and internal organ
system
– Simplest animals to have three embryonic germ layers
– Bilateral symmetry
– Cephalization—What is it?
• Concentration of sense organs and nerve cells at front of body
– Incomplete or absent gut- acoelomates
• Coelom- fluid filled body cavity surrounded by muscle
Groups of flatworms
• Groups of flatworms
– Turbellarians
– Flukes
– Tapeworms
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No circulatory or respiratory systems
Pharynx- muscular tube that extends out for
feeding
Flame cells- specialized cells that remove
wastes from body
Ganglia- group of nerve cells that controls
nervous system
Eyespot- group of cells that can detect
changes in amount of light in their
environment
Most are hermaphrodites that reproduce
sexually
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Hermaphrodite- individual with both male
and female reproductive organs
Some reproduce asexually by fissionorganism splits into 2
Muscle cells and cilia to move
Monsters Inside Me: Living with the Enemy |
Discovery Education
• Turbellarians- class Turbellaria
– Most common type-planarians
– Free-living
– Most live in marine or fresh
water- bottom dwellers
• Tapeworms- class Cestoda
– Long, flat, parasitic worms
– Adapted to life inside of intestines
of host
– Scolex enables worm to hook to
host
– Proglottids- segments that make
up body
• Contain both male and female
reproductive organs
– No eyespots
– No mouth, grastrovascular cavity,
or digestive organs
– Hermaphrodites
– Raw or undercooked food
• Flukes- class Trematoda
– Parasitic flatworms
– Infect internal organs of
host
– No eye spots
– Hermaphrodites
– Burrow into intestines
and release embryos
into intestine- passed
out with feces
Sec 2- Roundworms
• Phylum Nematoda
• Round worms have
– Unsegmented worms
– Bilateral symmetry
– Cuticle- tough outer skeleton,
must be shed to grow
– Most are free living – they are
more complex than parasiticWhy?
– Have pseudocoeloms and
digestive systems with 2
openings- mouth and anus
• Pseudocoelom- false coelom,
only partial with tissue dervived
from mesoderm
• Parasitic types includehookworms, trichinella,
pinworms
• How does one get
infected with
roundworms?
– Drinking contaminateed
water
– Eating contaminated
food
– Insect bites
What type of worm? How do you
know?
• Parasitic roundworms include trichinella, filarial, ascarid,
and hookworms
• Trichinosis- disease caused by trichinella, live in hosts
intestines
– Uncooked pork
• Filarial worms- live in blood and lymph vessels of birds and
mammals
– Tropical regions of Asia, transmitted by biting mosquitos
– Elephantiasis
• Ascarid worms- live in host’s small intestine
– Commonly spread by eating vegetables not washed properly
– Can reach 50 cm
• Hookworms- live in host’s intestines
– Burrow into skin and enter bloodstream
– Suck on host’s blood
Sec 3- Annelids
• Phylum Annelida
• Annelids have
– A true coelom
– Segmented bodies- What does that mean?
– Closed circulatory system-blood contained w/in
network of blood vessels
– Separate sexes and hermaphrodites
• There are three groups of annelids
– Earthworms- Why are they important?
– Marine worms
– Leeches- external parasites
• Long and narrow segmented
bodies
– Septa- internal walls that
separates the body into
segments
– Setae- bristles that are
attached to each segment
• Nephridia- excretory organs
that excrete nitrogen
containing wastes
• Clitellum- band of thickened,
specialized segments that
secretes mucous that
contains eggs and sperm
Groups of Annelids
• Oligochaetes- class Oligochaeta
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Earthworms and relatives
Typically have streamline bodies
Relatively few setae compared to polychaetes
Most live in soil or freshwater
• Leeches- class Hirudinea
– External parasites that suck blood and body fluids of their host
– Live in moist habitats in tropical countries
• Polychaetes- class Polychaeta
– Sandworms, bloodworms, and relatives
– Marine annelids
– Have paired, paddlelike appendages tipped with setae
Sec 4- Mollusks
• biology: the science of life: world of animals | Discovery
Education
• Phylum Mollusca
– One of oldest and most diverse phyla
• Mollusks have
– Soft-bodies with a true coelom
– Usually have internal or external shell
• Most mollusks are classified into 3 of 7 classes
– Gastropods
– Bivalves
– Cephalopods
• Trochophore- free-swimming larval stage
– Characteristic of aquatic mollusks and annelids
Form and function in mollusks
• Mollusks share at least one of three features
– Radula
– Mantle
– Ctenidia
• Body plan of most mollusks
– Foot, mantle, shell, visceral mass
• Radula- flexible tongue shaped structure used for feeding by mollusks
• Octopi use sharp jaws to eat prey
• Clams, oysters, and scallops are filter feeders
– Siphon- tube-like structure through which water enters and leaves the body
• Open circulatory system- blood is pumped through vessels by a simple
heart
– Bivavles and Gastropods have open circulatory system
– Cephalopods have closed system- Why is closed system more beneficial to
them?
Groups of Mollusks
• Gastropods- class Gastropoda
– Pond snails, land slugs, sea butterflies, sea hares
– Shell-less or single shelled mollusks
– Move by using muscular foot located on ventral side
• Bivalves- class Bivalvia
– 2 shells that are held together by one or two powerful muscles
– Clams, oysters, mussels, and scallops
• Cephalopods- class Cephalopoda
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Most active
Octopi, squids, cuttlefishes, nautiluses
Soft bodied mollusks in which head is attached to single foot
Foot is divided into tentacles or arms