Large, muscular tubes that alternately contract and relax,
keeping the blood flowing, Throat cavity; used by earthworms to
suck in soil Tube like structure through which soil and food
particles pass A round organ used to temporarily store food A
muscular organ containing grains of sand used to grind up food
Muscles used to make the body longer by tightening Muscles that
when contracted shorten the body Bristles used for locomation
Openings where sperm cells are received; the sperm cells will
fertilize eggs as they are laid A swelling that produces a
protec6tive slime ring that covers the fertilized eggs as they are
laid One of many openings through which wastes are passed to the
outside of the body
Slide 3
Lumbricus terrestris is the scientific name of the common
earthworm. An earthworm does not have a separate head or any
visible sense organs.
Slide 4
For purposes of studying earthworms, biologists assign numbers
to the body segments. Segment number 1 is found at the anterior end
(mouth end). 1. Prostomium 8. Dorsal blood vessel 2. Mouth 9.
Ventral blood vessel 3. Buccal cavity 10. Aortic arches 4. Pharynx
11. Suprapharyngeal ganglion 5. Esophagus 12. Circumphar.
connective 6. Nephridia 13. Ventral nerve cord 7. Seminal vesicles
Segments 1-12
A distinct swelling involved in reproduction called the
clitellum is found at earthworm segments 32-37.
Slide 7
The complicated organs of the digestive system take up most of
the anterior half of the earthworms body.
Slide 8
Slide 9
Since it has no jaws or teeth, the earthworm uses its muscular
pharynx to suck in soil. The earthworm ingests large amounts of
soil, which has organic matter in it. The food particles and soil
go through a tubelike esophagus into a round organ called a crop.
The crop stores the food temporarily. Other animals with a crop:
Birds
Slide 10
Food leaving the crop is forced in a very muscular organ called
the gizzard. What does it do? Contracting and expanding of the
gizzard grinds up organic matter into smaller pieces so digestion
can occur. Food is digested in the intestine (segment 19 to end)
and the digested food is absorbed by the blood circulating through
the intestinal wall.
Slide 11
Earthworms have a circulatory system comparable to higher, more
complex animals. They are said to have a closed circulatory system.
What is a closed circulatory system? A system in which blood is
contained within a network of blood vessels.
Slide 12
Even though they have the kind of circulatory system found in
many higher animals, it is just a simple version of it. For
instance, their aortic arches, which are comparable to our heart,
do not contain any chambers or valves.
Slide 13
What is an open circulatory system? A system in which blood is
not always contained within a network of blood vessels What type of
organisms do you think have open circulatory systems? Mollusks and
arthropods are groups of animals that have an open circulatory
system.
Slide 14
How do earthworms breathe? A thin skin enables worm to absorb
oxygen and give off carbon dioxide diffusion Why must their skin be
kept moist? Diffusion or exchange of gases will not occur if worm
is not moist How do they keep their skin moist? A mucus is secreted
by the epidermis (skin cells)
Slide 15
Wastes are passed to the outside of the body through nephridia.
There are two nephridia in each segment except the first three and
the last. Each nephridium does the same kind of work that a kidney
does in a mammal.
Slide 16
A large collection of nerve cells called the cerebral ganglion
functions as the brain of the earthworm. Though the earthworm does
not have eyes or ears, it is sensitive to light and vibrations.
Other receptors sensitive to touch, chemicals, and changes in
temperature are scattered through the epidermis (skin).
Slide 17
To shorten its body, the earthworm contracts its lengthwise or
longitudinal muscles. To lengthen its body, the earthworm contracts
its circular muscles.
Slide 18
Earthworms are hemaphroditic, but they do not self-fertilize.
The earthworm stores its sperm in sacs called seminal vesicles,
located in segments 9, 10 and 11.
Slide 19
Eggs are produced in a pair of small ovaries in segment 13.
During sexual reproduction, two earthworms lie next to each other
and swap sperm.
Slide 20
The sperm from one worm enters the other and is collected and
stored in seminal receptacle.
Slide 21
Sperm leaving the seminal receptacles is put into a slim ring
produced by the clitellum (swelling). The eggs will be fertilized
in the slime ring, which will slip off the body and protect the
young worms as they develop.