Transcript Phylum Annelida

Vocabulary List








Crop
Gizzard
Nephridia
Setae
Clitellum
Metamerism
Parapodia
Tagmatization
Chapter 13
Characteristics of
Phylum Annelida





Body is metameric (segmented
arrangement of body parts)
Bilateral symmetry and wormlike
Closed circulatory system
Includes over 10,000 species of
segmented worms-most are marine
Triploblastic Coelomates
Characteristics of
Phylum Annelida
Live everywhere except in frozen
soil of polar regions and in the sand
of dry deserts
 Include earthworms, marine worms,
and parasitic leeches
 Different from flatworms and
roundworms because they are
segmented and have a coelom

Taxonomy of Annelida:
Kingdom
Animalia
Phylum Annelida
 Class Polychaeta
 Class Clitellata
Class Clitellata
 Characteristics:
 Clitellum in cocoon formation
 Monoecious
 Few or no setae
 Two
subclasses:
 Oligochaeta (earthworms)
 Hirudinea (leeches)
Subclass
Oligochaeta
Over 3,000
species
 Habitat:





Freshwater
Few estuarine
Some marine
Terrestrial
 live in soil
 during hot weather,
may burrow 3
meters down
Lumbricus
terrestris
Earthworm
No parapodia
Cuticle covers body
Body segmented with
short setae
 Clitellum:




 Swollen set of segments in
the anterior half
 Will secrete mucus during
copulation
 Forms a cocoon
Subclass Hirudinea
Leeches
About 500 species
Most are freshwater
Predators of small
invertebrates
 Feed on body fluids
of vertebrates
(parasites)




Class Polychaeta
Largest class
(more than 5,300
species)
 Mostly marine
 Habitat:

 ocean floor
 Under rocks,
shells
 Crevices of coral
reefs
 Burrow through
substrate
(tubeworms)
Segments with extensions called
parapodia
 Numerous setae (bristles)
 First body segment called the
peristomium:

 has mouth, protomium, sensory tentacles (cirri) & 2
to 4 pairs of eyes

May be predators, herbivore, scavengers,
or filter-feeders
Metamerism & Tagmatization
Segmental arrangement
of body parts in an
animal.
 It influences every
aspect of annelid
structure & function
 The
compartmentalization of
the body has resulted in
each segment having its
own excretory, nervous,
and circulatory
structures.

The specialization of
body regions in a
metameric animal.
 Although it is best
developed in the
arthropods, some
annelids also display
tagmatization.
 Greek “tagma” means
arrangement

Advantages of
Metamerism (segmentation)

Creation of hydrostatic compartments

Lessens the impact of injury

Permits the modification of certain regions
of the body for specialized functions, such
as feeding, locomotion, and reproduction.
Feeding & Digestion


Running through all
earthworm segments
from the mouth to the
anus is the digestive
tract (a tube in a tube)
Food and soil taken in by
the mouth pass through
the pharynx into the
crop, where they are
stored until they pass to
the gizzard (gizzard is a
muscular sac containing
hard particles that help
grind soil and food
before they pass into the
intestine).
Feeding & Digestion



Nutrients are
absorbed from
the intestine
Undigested
material passes
out of the
worm’s body
through the
anus
Parasitic
annelids have
pouches along
the digestive
tract that hold
enough food to
last for months!
Circulation





Closed circulatory system. Oxygen and nutrients move
to various parts of their bodies through their blood
vessels.
At the same time carbon dioxide and metabolic wastes
are removed from the blood and excreted.
Some of the vessels at the anterior end, or head, are
large and muscular and serve as hearts that pump the
blood.
The blood moves toward the anterior end of the worm in
the dorsal blood vessel and toward the posterior end in
the ventral blood vessel.
An earthworm has five hearts that pump blood through
its circulatory system!
Respiration & Excretion
Segmented worms have 2 nephridia in
almost every segment.
 Cellular waste products are collected in
the nephridia and are transported in tubes
through the coelom and out of the body.
 Nephridia also function in maintaining
homeostasis of body fluids of annelids,
ensuring that the volume and composition
of body fluids are kept constant.

Response to Stimuli
Anterior segments are modified for
sensing the environment
 You might have seen an earthworm
quickly withdraw into its burrow when you
shine a flashlight on it or step close to
it….these observations show that
earthworms can detect both light and
vibrations.

Movement





When an earthworm moves, it contracts circular
muscles running around each segment.
This squeezes the segment and causes the fluid
in the coelom to press outward like paste in a
tube of toothpaste being squeezed.
Because the fluid in the coelom is confined by the
tissues between segments, the fluid pressure
causes the segment to get longer and thinner…
Next, the earthworm contracts the longitudinal
muscles that run the length of its body.
This causes the segment to shorten and return to
its original shape, pulling its posterior end
forward and resulting in movement!
Movement


Many annelids have setae on each segment.
Setae are tiny bristles that push into the soil
and anchor the worm during movement.
By anchoring some segments and retracting
others, earthworms can move their bodies
forward and backward segment by segment!
Annelids can reproduce both sexually and
asexually.
 Most annelids have separate sexes, but
some, such as earthworms and leeches,
are hermaphrodites.
Reproduction

 Sperm are passed between two worms near
segments called clitellum (a thickened band of
segments).
 It produces a cocoon from which young earthworms
hatch.
 Sperm and egg pass into the cocoon as it slips
forward off the body of the worm.
 After fertilization, the young are protected in the
cocoon as they develop.
Some annelids reproduce asexually by
fragmentation.
 If a worm breaks apart, the missing parts
can be regenerated.

Earthworm reproduction

Monoecious & Exchange sperm
Copulation: Two worms line up in opposite
directions
2. Clitellum of one lines up with genital segments of
other
3. Mucus holds worms together
4. Sperm travel from one to the other
5. Last 2-3 hours
6. After copulation, a cocoon is formed around
worm
7. Mucus, food, eggs and sperm are deposited in
the cocoon
8. Fertilization occurs in the cocoon
9. Worms back out of the cocoon and it drops to the
ground
10. Hatching – takes a few weeks
1.
Earthworms




Probably the best known annelids
Used as bait for fishing and are found in garden
soil.
Can eat its own mass in soil every day!
Earthworms ingest soil to extract nutrients…in
this way, earthworms aerate the soil-they
break it up to allow air and water to move
through it (my mom always said, you know
you’ve got good dirt if you find a worm)
Include bristleworms
and fan worms
 Have head regions with
well-developed sense
organs, including eyes.
 Most body segments
also have a pair of
appendages called
parapodia that are used
for swimming and
crawling
 Fan worms are sessile
and filter feeders, they
trap food in the mucus
on their fan-shaped
structures.
 If there is a threat
nearby, fan worms
retreat into their tubes.

Marine Annelids
Leeches







External parasites
Flattened bodies and usually no setae
Most live in freshwater streams or rivers
where they attach to the bodies of their
hosts-including fishes, turtles, and humans.
Leeches attach to their hosts using front and
rear suckers.
When a leech bites, it saliva contains
chemicals that act as an anesthetic.
Other chemicals in the saliva reduce swelling
and prevent the host’s blood from clotting.
They maintain blood flow after microsurgery.
Medicinal leeches

http://video.nationalgeographic.com/vide
o/player/places/countriesplaces/india/india_leechescure.html
http://www.leeches.biz/medicine-leech.htm