Download Unit 5 Notes #6 Segmented Worms - Mr. Lesiuk

Unit 5 Notes #6 - Phylum Annelida:
Segmented Worms
A) Body Plan:
Similarities To Phylum Aschelminthes
(Nematoda):
1. Bilateral symmetry
2. Three layers (Ectoderm, endoderm,
mesoderm)
3. Complete digestive system (mouth to anus).
Differences:
-Contains a “Coelom”, this is considered to be
a “True Cavity”. Unlike the “Pseudocoelom”,
this cavity is not just fluid-filled, but it is also
lined with mesoderm.
This provides several advantages:
1) This coelom separates the body wall from
the gut. Thus food does not interfere with
body movements.
2) The fluid in the coelom may circulate many
substances, including wastes, food and
dissolved gases in the body.
3) The coelom provides more space where
true systems and their organs can operate.
(Ex, stomach, heart, lungs etc.)
-Annelida are the first to exhibit
SEGMENTATION: “The repetition of body
units that contain similar structures. Most
segments contain duplicate structures for
locomotion, excretion, muscle and nervous
tissue.
-This segmentation is visible on the outside of
these worms.
B) Annelida Diversity:
1. Class Polychaeta: These are mainly marine
worms that live in sand or mud of shallow
coastal areas.
-They
usually have
pairs of paddlelike appendages
that are tipped
with numerous
bristles.
2. Class Oligochaeta: Most are terrestrial but
some are freshwater, found burrowed into
soil and mud.
-They do not have any leg-like appendages
but do have four pairs of bristle per segment.
Example : Earthworm
3. Class Hirudinea: These are the leeches.
-Most live in freshwater as external parasites.
-They have a sucker at each end of their
body, they secrete an anticoagulant and an
anesthetic to facilitate “blood sucking”
THE EARTHWORM
A) Digestive System of the Earthworm:
-Adapted for ingesting leaf fragments, seeds,
bodies of small animals and protists, as well
as rich organic soil.
-Soil and organic matter are sucked into the
mouth by the muscular pharynx.
-Muscular action pushes the food through the
narrow esophagus and into the crop for
temporary storage.
-The crop directs food matter into the
muscular gizzard.
-The gizzard, with help of sand particles,
grinds the food into smaller pieces.
-At this point the food is pushed into the
intestine, which extends from the gizzard to
the anus.
-Gland cells of the intestinal wall, contain
enzymes, which digest proteins, fats, and
carbohydrates, including cellulose.
-The digested nutrients are absorbed by the
blood, while waste passes out through the
anus.
-The muscular action that pushes the food
along is called peristalsis. It results from the
alternate contraction and relaxation of
certain muscles to create a wave motion along the
tube. Check out this link:
http://images.google.ca/imgres?imgurl=http://www.ncsu.edu/scivis/lessons/earthworm/Image5.gif&i
mgrefurl=http://www.ncsu.edu/scivis/lessons/earthworm/Overview.html&h=352&w=500&sz=19&tb
nid=oki0wkxCTUoJ:&tbnh=89&tbnw=126&start=2&prev=/images%3Fq%3DEarthworm%2BDige
stive%2BSystem%26hl%3Den%26lr%3D%26sa%3DG
B) Circulatory System of Earthworm:
- Need a closed circulatory system, as animals
get larger, simple diffusion of food, oxygen
and wastes can no longer meet the needs of all
body parts.
-Special circulatory tissue called blood is
directed through a continuous system of
muscular tubes called blood vessels. Blood is
red due to Hemoglobin.
-Blood flows through the dorsal (top/back)
vessel. From here, five pairs of beating aortic
arches (hearts) direct the flow to the ventral
(bottom/belly) vessel.
-In each segment, the ventral vessel branches
to send blood out to the body wall.
-Other branches take blood to the intestine
where the blood absorbs nutrients.
-Capillaries return the blood to the dorsal
vessel.
C) Respiration :
-This occurs by diffusion of oxygen and
carbon dioxide through the moist skin.
-Kept moist by mucous glands in the skin and
by the cuticle which prevents desiccation
(drying out)
D) Nervous System:
-Small brain is located above the pharynx, the
brain is attached to the ventral nerve cord,
which runs the length of the worm.
-In each segment there are sensory and motor
nerves that branch off of the ventral nerve
cord.
-These sensory receptors are sensitive to light,
touch, and a number of chemicals.
E) Reproduction in Earthworms:
- Earthworms are monoecious
(hermaphroditic).
The male system:
1. Two pairs of small testes to produce
sperms (segments 10 and 11)
2. Two large seminal vesicles store the sperm.
3. The openings of two sperm carrying tubes
called vasa deferentia are located on the
ventral side of segment 15.
The female system:
1. A pair of small ovaries in segment 13
2. Two pairs of seminal receptacles in
segments 9 and 10, which store sperm
received from another worm during mating.
- During the process of mating two worms
line up beside each other pointing in opposite
directions.
- The clitellum secretes a mucous sheath
around the two worms, this sheath will ensure
they stay together.
- Later each worm secretes a cocoon around
its clitellum, and eggs from the oviducts are
passed into the cocoon.
- The worm backs out of the cocoon; as the
cocoon passes the openings of the seminal
receptacles, sperm stored from the mating is
released into the cocoon.
- Fertilization now takes place in the cocoon.
- When the worm leaves the coccoon, the ends
of the coccoon close over.
- The young worm emerges from the cocoon
in 2-3 weeks, it appears similar to the adult
stage.
- Worms do not develop a clitellum until they
are sexually mature.
OVERALL : EARTHWORM ANATOMY