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There are ~ 12,000 annelid species in 2 classes.
Exam 3 Mar 22
Cycloneuralia
Mollusca I
Mollusca II
Mollusca III
There are ~ 12,000 annelid species in 2 classes.
Annelids are triploblastic protostomes with true coeloms.
Gastrula
Clitellata
~4,000 spp.
Polychaeta
~8,000 spp.
Blastopore
Mouth
1
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Annelids share 4 features
1. Setae
Annelids share 4 features
2. Metamerism
Annelids share 4 features
2. Metamerism
Annelids share 4 features
3. Movement via circular & longitudinal muscles
Circular muscles
segments
Longitudinal muscles
septa
Earthworm cross section
2
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Annelids share 4 features
3. Movement via circular & longitudinal muscles
Annelida is divided into 2 classes.
Polychaeta
Annelids share 4 characteristics.
4. Closed Circulatory System
Class Polychaeta have many setae on parapodia.
Clitellata
segments
Many setae on parapodia
Few setae; no parapodia
Clitellum for reproduction
Parapodia
with setae
Nereis Sense organs &
mouth
3
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Parapodia are un-jointed appendages that bear setae.
Polychaetes can be motile (can move around) or sedentary
(anchor to substrate).
setae
Acicula
A benthic motile
polychaete with
many parapodia & setae
A polychaete parapodium under a microscope
Tube worms are marine polychaetes that have adapted to live along
deep-sea hydrothermal vents. Tube worms are peizophiles.
Sessile infaunal
christmas tree worms
that live in coral
Tube worms have chemosynthetic bacterial endosymbionts.
Bacteria
Tubeworms
Bacteriocytes
https://www.youtube.com/watch?v=dg6ZewBTRj8
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Class Clitellata have few setae, no parapodia and reproduce
via the clitellum. This class includes earthworms & leeches.
Clitellata mate via the clitellum.
Clitellum
Earthworm egg case
Subclass Oligochaeta includes earthworms.
Earthworms play a critical role in
ecosystems.
Few setae
5
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However, invasive earthworms have over populated some U.S. forests.
Thick, healthy leaf litter layer
(dark brown) prior to
earthworm invasion.
When leaf litter is broken down too quickly, native plant
populations are reduced.
Very thin leaf litter layer, most of
which has been converted to soil
(dark brown) after earthworm
invasion.
Some species of earthworms are used in
vermicomposting.
Subclass Hirudinea are the leeches. Most leeches are hematophagous
ectoparasites of both vertebrates & invertebrates.
6
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Historically, leeches were used in a medical process called blood-letting.
Recently leech therapy has been used in modern operating rooms.
Hirudo medicinalis - medicinal leech
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