Annelids: Segmented Worms
Phylum Annelida
1.
_____________________ from the Latin word ________________ meaning “little ring”
2.
All are ________________________ worms
3.
Approximately __________________ species including earthworms, freshwater worms, leeches,
and marine worms
4.
Annelid Characteristics

_________________________: 3 cell (body) layers

Highest level of organization: _____________________

Bilateral symmetry

Cephalization

Eucoelomate
o Have a true body cavity that is completely surround by ____________.
o Draw the coelom below:

The Coelom
o The coelom is a closed, fluid filed cavity that surrounds the gut.
o The fluid within acts as a ______________________________ (blood)
o

Tissue membranes (____________________) suspend the organs in the coelom
Metamerism
o The body is made up of serially repeating coordinated segments called
_____________________ that are separated from one another by _________________.
o
Each metamere contains sets of repeating organs. Ex. Gut, blood vessels, nerve
cord, excretory organs.

Two part head consisting of:

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_____________________________: fleshy lobe
that overhangs the mouth
o _____________________________: first body
segment
___________________: circular rings
_________________________: the last segment where
the anus is
_________________________: reproductive
structure
Nervous System
o
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
2 cerebral ganglia
A ventral nerve cord with two ganglia per metamere
In some species, sensory organs such as _____________, ____________, and
__________________ have arisen.
(________________ are appendages that may or may not be covered in cilia that help
the worm find and pull in food)
Locomotion
o Both _____________________ and ________________ muscles
o Most have _____________ (chitonous bristles secreted by the epidermis) that aid in
locomotion and burrowing
o Setae may be modified into appendages called ___________________
Skeletal System
o Fluid in the coelom acts as a _______________________________
o
o
o
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
PARAPODIA


Gas Exchange
o Mainly by ____________________ through skin
o Class Polychaeta often has specialized structures for gas exchange (ex. Parapodia,
gills)
Digestive System
o ____________________________
o


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5.
Regional ________________________ (digestive organs)
Circulatory System
o ________________ circulatory system composed of blood vessels (some of which are
contractile and act as “hearts”)
o Some circulation is also accomplished by the _________________ fluid
Excretion
o Excretion is accomplished by organs called _______________________ (singular
nephridium)
Reproduction
o Sexual
Three Classes of segmented worms
 _________________________________

_________________________________

_________________________________
Class Polychaeta
Characteristics
•
All _________________
•
This class contains 2/3 of all known Annelids
•
Common species are _________________ , ___________________ , and _____________________
•
Have a well developed head with specialized sense organs
•
Commonly called _____________________________ because….
o
Have many ________________ (chitonous bristles secreted by the epidermis)
o
(Poly = many, chaeta= setae)
o
These setae are arranged in bundles on paddle-like appendages called
____________________
o
•
The parapodia function in ______________________, locomotion, and __________.
_____________________ (tagmosis): the fusion and specialization of formerly metameric
segments
•
Many are ____________________ feeders with specialized structures
•
Many are __________________________ with specialized structures
•
Many construct their own homes out of __________ (calcium carbonate), __________________,
and _______________________.
•
Reproduction
o
Usually ___________________
o
No permanent sex organs; gametes are shed into coelom
where
they stay until time for fertilization
o
Fertilization is usually ___________________ in water
o
________________ development  __________________ larvae
swims
around until it grows into adult for by adding segments
•
Ecology
o
o
Polychaetes often have effective defense strategies:

some have tubes to hide in

some have vicious jaws

some have modified “stinging” setae
Some Polychaetes have a mutualistic relationship with their host

For example, many scaleworms are found near, or in the mouth, of brittlestars,
starfish, and sea urchins.

The scaleworm eats its host’s leftovers and with its vicious jaws, it will attack
any predator trying to eat it’s host.
Class Oligochaeta
Characteristics

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Earthworms are the most common
Habitats: __________________________, freshwater, and __________________
Have few setae (“Oligo” = ________________, “chaeta” = setae
Usually feed on ___________________________ (decaying organic matter)
Depends on habitat, but they can feed on…
o Dead leaves and plant roots
o Living things such as other worms, bacteria and fungi


o Decomposing remains of other animals
Do earthworms eat dirt?
o Yes and n.
o Earthworms ________________________ dirt as they burrow, so yes they swallow it.
o HOWEVER, they do not get ______________________ from dirt. Their nutrients come
from decaying plant and animal remains that are in the dirt.
Earthworms have a specialized digestive system to obtain the maximum amount of nutrients
out of the detritus.
o Example: pharynx, crop, gizzard, etc.

Locomotion
o Circular muscles contraction
o Longitudinal muscle contraction

Reproduction
o Usually ________________________
o Still have to have a partner

o Cross-fertilize by exchanging _______________.
Ecology
o Earthworms are essential soil ___________________, meaning they allow air to enter the
soil.
o
Mix the soil with their tunnels.
o
Worm feces are great plant food = ____________________!
Class Hirudenia

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

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Includes ____________________.
Usually freshwater but there are some ____________________ and
terrestrial species.
No __________________ between metameres
No ___________________ or parapodia
Have two suckers
Have an extendable ____________________ for feeding
Usually have a fixed number of segments (34). Each metamere
consists of several annuli
Lack septa between metameres, so they are incapable of moving
like Oligochaetes.
Instead, they use their anterior and posterior suckers to move.
Reproduction
o usually _________________________
o
cross-fertilize by exchanging sperm
Ecology
o Although some leeches are parasitic blood suckers (can be temporary or permanent),
many are predators.
o Leeches have been used medicinally since the 19th century.
o
Currently they are used to increase blood flow following reconstructive surgery
o
_______________________ is a powerful anticoagulant that is found in the salivary glands
of leeches