Transcript Earthworms

Chapter 11, Phylum Annelida
(Segmented Worms)
Phylum Annelida
Phylum Annelida
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Body of annelids have metamerism.
Metamerism is a characteristic that features
regularly repeating body segments.
This phylum includes earthworms and
freshwater worms (Oligochaeta), leeches
(Hirudinea), and marine worms (Polychaeta)
Annelids are sometimes called “Bristle worms”,
because of the tiny chitonous bristles that they
bear (except leeches) called setae.
Important Characteristics of
Phylum Annelida
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Metamerism or
segmentation
Epidermal chitonous
setae (except in
leeches)
Fleshy appendages
called parapodia in
some annelids
Coelomate body cavity
Annelid Ecology
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Annelids are found in the ocean, freshwater, and
in terrestrial soil.
Often live in burrows in the ground and feeds on
organic matter in soil.
Others feed on suspended particles that are
trapped on parapodia.
Some are predaceous, and hunt by hiding in rocks
and corals ambushing their prey.
Others are bloodsucking carnivores (leeches).
Annelid Ecology
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The importance of earthworms in terrestrial
ecosystems can not be overstated.
Without earthworms, plants would not be able to
grow, and the entire food chain would be impacted.
Earthworms help aerate, fertilize, mix, and provide
proper drainage to soils.
Leeches are sometimes used in the medical field
when fingers or toes are cut off. Leeches can help
stop the bleeding at the wound while veins and
arteries are still healing.
Earthworms and Medical Leeches
Annelid Anatomy and Locomotion
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The body of an annelid usually consists of a two-part
head (prostomium and peristomium), a series of
body segments (called metameres), and a terminal
segment called the pygidium.
Annelids have both longitudinal and circular
muscles which create waves of expansion and
contraction when they move called peristalsis.
Class Polychaeta
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Name means “many + long hairs”.
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Many setae per body segment.
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Mostly marine and dioecious.
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Most segments with parapodia used for crawling,
swimming, feeding and respiration.
Examples include the clam worm, scale worms, fireworms,
fanworms (or featherdusters).
Class Oligochaeta
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Name means “few + long hairs”.
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Few setae per body segment.
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Terrestrial and freshwater.
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No head or parapodia.
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Coelom divided by septa.
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Hermaphroditic
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Earthworms
Earthworms
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Earthworms (also known as nightcrawlers) burrow
in moist soil and emerge at night to feed on
detritus and vegetation and to breed.
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Earthworms are usually about 12 – 30 cm long.
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Giant tropical earthworms can get 3 – 4 meters.
Earthworm Anatomy
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Setae project through small pores in the
cuticle to provide anchoring points when
the earthworm moves or burrows.
Food is brought in by a muscular pharynx
The digestive tract is unsegmented and
runs continuously the length of the body.
The intestine has a u-shaped fold called a
typhlosole that increases surface area.
Earthworm Digestive System
Earthworm Anatomy
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Earthworms also have a crop and a gizzard,
which stores and mechanically digests food.
Annelids have closed circulatory systems.
Earthworms have five (aortic arches) hearts. The
dorsal blood vessel is the main blood vessel.
The excretory system consists of a pair of
nephridia (similar to our kidneys) in each body
segment (except the first three and last one).
Earthworm Circulatory/Excretory
System
Earthworm Anatomy
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The nervous system in earthworms and all
annelids have a pair of cerebral ganglia.
Posterior to the cerebral ganglia, ventral nerve
cords run the length of the body and each body
segment has its own pair of smaller ganglia.
Earthworms are hermaphrodites and exchange
sperm with each other during copulation.
When earthworms mate, they come out of their
burrows at night and touch ventral surfaces.
Earthworm Nervous System
Earthworm Reproduction
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Mating earthworms are held together by mucus
secreted by a reproductive organ called a clitellum
and they are also held together by ventral setae.
Sperm are discharged and travel to an opening
called the seminal receptacle.
After sperm exchange, the worms separate.
Each worm then secretes a protective covering over
the clitellum that forms a cocoon.
Earthworm Reproduction
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The cocoon slides forward along the body
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As it slides forward, it passes over the oviducts.
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Eggs from the oviduct and sperm from the
seminal receptacles transfer into the cocoon.
After fertilization the cocoon slides off the worm.
The embryos develop in the cocoon and
eventually emerge as juvenile worms.
Earthworm Reproduction
Class Hirudinea
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Name means leeches
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Mostly freshwater, some marine and terrestrial.
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Body usually with posterior and anterior suckers
that secrete anticoagulants and consume blood.
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No parapodia or setae
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Clitellum present
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Hermaphroditic