Download Unit 8 Invertebrates - Jamestown Public Schools

Unit 8 Invertebrates
Ch. 27 Worms & Mollusks
What Is a Flatworm?
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Flatworms are soft, flattened worms that
have tissues & internal organ systems
They are the simplest animals to have 3
embryonic germ layers, bilateral
symmetry, & cephalization
Form & Function in
Flatworms
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Parasitic worms feed on blood, tissue
fluids, or pieces of cells within the host’s
body
Blood flukes are parasitic flatworms that
mature in the blood vessels of humans
Form & Function in
Flatworms
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All flatworms, including this planarian,
have organ systems that perform essential
life functions
Groups of Flatworms
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The 3 main groups of flatworms are
turbellarians, flukes, & tapeworms
Turbellarians are free-living flatworms
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Most live in marine or fresh water
Groups of Flatworms
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Flukes are parasitic flatworms
Most flukes infect the internal organs of
their host
Groups of Flatworms
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Tapeworms are long, flat, parasitic worms
that are adapted to life inside the
intestines of their hosts
What Is a Roundworm?
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Most roundworms are free-living,
inhabiting soil, salt flats, aquatic
sediments, & water, from polar regions to
the tropics
Many others are parasitic & live in hosts
that include almost
every kind of plant &
animal
What Is a Roundworm?
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Roundworms are unsegmented worms
that have 2 openings, a mouth & an anus
Roundworms & Human
Disease
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Parasitic roundworms include trichinosiscausing worms, filarial worms, ascarid
worms, & hookworms
Trichinosis-causing worms
reproduce in the intestines
of their host & then form
cysts in their muscle tissue
Roundworms & Human
Disease
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Filarial worms are found mainly in the
tropics
They are transmitted from 1 host to
another through biting insects
Ex.) Elephantiasis
Roundworms & Human
Disease
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Ascarid worms absorb the host’s digested
food & can cause severe malnutrition
Blockage of the intestine can be so severe
that it can cause death
What Is an Annelid?
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Annelids are worms with segmented
bodies
They are also called segmented worms
because the body is divided into many
similar segments
Form & Function in Annelids
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Feather-duster worms exchange gases
underwater using feathery gills
Form & Function in Annelids
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Some annelids, including earthworms, are
hermaphrodites - each worm produces
both egg & sperm
During mating, the worms exchange
sperm, which will be used to fertilize egg
cells
Earthworm
Groups of Annelids
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There are 3 main classes: oligochaetes,
leeches, & polychaetes
Oligochaetes have few setae, & live in soil
or fresh water
Groups of Annelids
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Leeches are typically external parasites
that suck the blood & bloody fluids of their
host
Groups of Annelids
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Polychaetes are marine annelids have
paired, paddlelike appendages tipped with
setae
Ex.) Fireworm
Ecology of Annelids
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Most annelids spend their lives burrowing
through soil, aerating it, & mixing it
Their tunnels provide passageways for
plant roots & water, & allow
the
growth of beneficial
oxygenrequiring soil bacteria
What Is a Mollusk?
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Mollusks are soft-bodied animals that
usually have an internal or external shell
Form & Function in Mollusks
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The body plan of most mollusks includes a
foot, mantle, shell, & visceral mass
Form & Function in Mollusks
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Mollusks have evolved a variety of ways of
responding to potential danger
Snails withdraw into their shells
Octopi & squids squirt ink from their
digestive tracts, causing temporary
numbness of
predators
Groups of Mollusks
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The 3 major classes of mollusks are
gastropods, bivalves, & cephalopods
Gastropods are shell-less or single-shelled
mollusks that move by using a muscular
foot
Groups of Mollusks
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Members of the class Bivalvia have 2
shells that are held together by 1 or 2
powerful muscles
Includes: clams, mussels, oysters, &
scallops
Groups of Mollusks
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Cephalopods are typically soft-bodied
mollusks in which the head is attached to
a single foot
The foot is divided into tentacles or arms
Nautiluses are the most
primitive
group of
cephalopods
Groups of Mollusks
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Cephalopods have the most complex
nervous system of all the mollusks, with a
highly developed brain & sense organs,
like the eye of a squid
Ecology of Mollusks
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Mollusks are important source of food for
many organisms, including
humans