Earthworms
Earthworms are classified as Annelida. Annelida
mean little rings which
refers to the many segments in their body. The
structure of an earthworm’s
body is made up of more than one hundred segments
separated by partitions that
divide the coelum. All segments are identical
except by the anterior and
posterior ends. The anterior segments reflect the
cephalization that is an
adaption of burrowing. The head of the earthworm
contains the sense organs. The
muscle lines that make up the interior body
wall are circular and longitudinal.
Earthworms move by anchoring some
segments by their setae and contracts the
circular muscles in front of those
segments, producing fluid pressure in the
anterior coelom cavities. The
anterior setae grip the ground, the longitudinal
muscles contract pulling the
posterior along. Earthworms burrow and feed on soil
and organic matter at the
same time. They digest the organic matter and
eliminate wastes and undigested
matter as dirt and feces called castings.
Earthworms are good for the
soil because they sucked up soil into the by the
muscular pharynx. The soil
then passes through a tubelike esophagus to a
temporary storage called a
crop, and from there to the gizzard. The gizzard
walls grind the soil,
releasing and breaking up organic matter. Through the
earthworm’s body via a
closed circulatory system it transports oxygen,
nutrients, and wastes. The
blood travels from the anterior to the posterior
through ventral blood vessel
and then forward through a dorsal vessel. Aortic
arches are five tubes that
link the major vessel near the anterior. Smaller
vessels branch into each
segment of the body. Earthworms have no respiratory
system or no gills.
Carbon dioxide and oxygen diffuse directly across the skin.
This process
can only happen if the skin is moist. Earthworm’s secretions of
mucus and a
thin cuticle help keep the skin moist. Through a long tube called
nephridia
the earthworms eliminate nitrogenous wastes. Earthworms are sensitive
to
touch, light, vibrations, moisture, chemicals, and temperatures. Other
sense
organs and the nerves that control individual muscle contractions are
present in
each segment. Earthworms are hermaphrodites, but one worm cannot
fertilize it
own eggs. When earthworms are join to head to tail it’s called
mating.
Together they form a mucus around each other. They both inject
sperm into the
mucus. One of their sperms goes to a pouchlike seminal
receptable. After a
several days a mucus and chitin sheath is secreted by the
clitelllum a swelling
around the sex organs. When the worm wriggles to slip
the sheath off its body,
eggs, and sperm are joined and fertilization
occurs.