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Segmented Worms- Phylum Annelid Notes
Name _________________
Annelids are worms with _________________ bodies. They have a true _____________ that is lined with
tissue derived from mesoderm.
Three Germ Layers of an Annelid
The body of an annelid is divided into segments.
Each segment is separated by ______________, which are internal walls between each segment.
Body segments may carry eyes, antennae, other sense organs, or be specialized for functions such as respiration.
Bristles called ____________ may be attached to each segment.
Annelids have a ______________________ digestive tract that food passes through from the mouth to the anus.
Feeding and Digestion
In carnivorous species, the _______________ usually holds two or more sharp jaws that are used to attack prey.
Annelids that feed on decaying vegetation have a pharynx covered with sticky mucus.
Other annelids obtain nutrients by ___________________________.
In earthworms, the pharynx pumps food and soil into the esophagus.
The food then moves through the ____________, where it can be stored.
It then moves through the ________________, where it is ground into smaller pieces.
The food is absorbed farther along in the digestive tract in the intestine.
Circulation
Annelids typically have a closed circulatory system, in which ______________ is contained within a network of
blood vessels.
Blood in the dorsal (________) vessel moves toward the head of the worm.
The dorsal blood vessel functions like a heart because it contracts rhythmically and helps _________ ________.
Blood in the ventral (___________) vessel runs from head to tail.
In each body segment, a pair of smaller blood vessels connect the dorsal and ventral blood vessels and supply
blood to the internal organs.
Respiration
______________ annelids often breathe through gills.
A gill is an organ specialized for the exchange of gases underwater.
_________-______________ annelids take in oxygen and give off carbon dioxide through their moist skin.
Excretion
Digestive waste passes out through the ____________
Cellular waste containing nitrogen is eliminated by nephridia.
______________ are excretory organs that filter fluid in the coelom.
Response
Most annelids have a well-developed nervous system consisting of a ________ and several ________ _______
Movement
Annelids have two groups of body muscles that function as part of a ____________ ___________.
Longitudinal muscles run from the front of the worm to the rear and can contract to make the worm shorter and
fatter.
Circular muscles wrap around each body segment and can __________ to make the worm longer and thinner.
The earthworm moves by alternately contracting these two sets of muscles.
Reproduction
Most annelids reproduce ______________
Some species use external fertilization and have separate sexes.
Other annelids are __________________. Two worms attach to each other, exchange sperm, and then store the
sperm in special sacs.
When eggs are ready for fertilization, a _________________ secretes a mucus ring into which eggs and sperm
are released.
A clitellum is a __________________________________________________.
After eggs are fertilized in the ring, the ring slips off the worm's body and forms a protective cocoon.
Young worms hatch weeks later.
Groups of Annelids
What are the characteristics of the three classes of annelids?
Groups of Annelids
Annelids are divided into three classes
•__________________
•__________________
•__________________
Oligochaetes
Oligochaetes contains _________________ and their relatives.
Oligochaetes typically have streamlined bodies and relatively few setae compared to polychaetes. Most
oligochaetes live in soil or fresh water.
Leeches
The class Hirudinea contains the ____________.
Leeches are typically external _____________ that suck the blood and body fluids of their __________.
Groups of Annelids
Leeches have powerful suckers at both ends of their bodies that help them cling to their hosts.
Some leeches force a muscular extension called a proboscis into the tissue of their host.
Others slice into the skin with a razor-sharp pair of __________.
The leech uses its pharynx to suck blood from the wound.
Some leeches release a substance that __________________ the wound—keeping the host from knowing it has
been bitten.
Leeches were once used to treat medical conditions.
Ecology of Annelids
Earthworms and many other annelids spend their lives burrowing through soil, ______________ and mixing it.
Earthworms help plant matter _________________.
Earthworm castings are rich in ____________,_______________, __________________, _______________,
and beneficial _________________