Earthworms
Phylum Annelida
Earthworms are the most highly developed worms. They are divided into segments or parts
called septa. They are found in salt and fresh water as well as in the soil. Earthworms are
helpful to man as bait for fishing and more importantly, because they loosen the soil for
roots to grow.
There are 2700 species of earthworms. Earthworms have many enemies including animals
that eat them and man who uses them.
System Type
Annelids System
Muscular-Skeletal
Annelids do not have a skeleton, but they do have two sets
of muscles [one that makes them long & thin, the other
makes them fat & scrunched]. It has bristles on each
segment called setae that help the earthworm move.
Digestion
Annelids have a digestive system. They eat dirt, digesting
the plant and animal matter in the dirt and then eliminates
the rest. They havev an esophagus for the food to go down,
a crop to store the food in, a gizzard that grinds the food
down, intestines for the food to pass through and take out
nutrients and an anus for the food to come out.
Nervous
Annelids have a nervous system with a ganglia [simple
brain] and nerve cord.
Circulation
Annelids have blood and blood vessels with multiple (5)
hearts.
Respiration
Annelids have no respiratory system. They take in oxygen
directly through its skin and gives off carbon dioxide
through diffusion. Its skin is always moist.
Reproduction
Annelids have both sets of sex organs [hermaphrodites], but
they must copulate with another worm to reproduce.
Excretion
Annelid’s wastes help to fertilize the soil. It gets rid of its
wastes through tubes that lead to pores that allow the
wastes out.
Symmetry
Annelids have bilateral symmetry.
Coloration
Annelids are generally colored in earth-tones such as
brown, tan, etc.. They can be up to eight feet in length!
EARTHWORM [ANNELID – SEGMENTED WORM]
Earthworms (also called nightcrawlers) are very
important animals that aerate the soil with
their burrowing action and enrich the soil with
their waste products (called castings). Good
soil can have as many as as 1,000,000 (a million)
worms per acre.
There are over 3,000 species of earthworms
around the world. These invertebrates (animals
without a backbone) range in color from
brown to to red, and most have a soft body.
Earthworms range in size from a few inches
long to over 22 feet long. The largest
earthworms live in South Africa and Australia.
Anatomy and Diet: The brain, hearts, and
breathing organs are located in the first few segments of the worm. It has five pairs of hearts! The rest of
the inside of an earthworm is filled with the intestines, which digest its food. Earthworms eat soil and the
organic material in it - like insect parts and bacteria. The mouth is covered by a flap (called the
prostomium) which helps the earthworm sense light and vibrations. Tiny bristles (called setae) are on most
segments of the earthworm's body.
Reproduction: Although each earthworm is hermaphroditic (having both male and female reproductive
systems), it takes two worms to mate and reproduce. The reproductive organs are in the clitellum (the
enlarged segments in the middle of an earthworm). The clitellum later forms a cocoon which protects the
developing eggs.
Earthworm Anatomy
External Anatomy – use the terms to label the picture to the
right.
Locate the two openings on the ventral surface of the
earthworm.
Note the swelling or band on the earthworm near its
anterior side [farther forward] - this is the clitellum.
The openings toward the anterior of the worm are the
sperm ducts. The openings near the clitellum are the
genital setae.
Locate the worm's mouth.
Circulatory system
Segmented worms have a closed circulatory system. This means that the blood is at all times closed within
vessels and transported around the organism’s body. They have blood vessels that are near their backside
and also near their belly-side.
Nervous System
Annelids have a nervous system composed of nerve cords that run the length of the worm on its belly-side.
It does not have a real “brain” – but the nerve cords to come together to form a ganglia [primitive brain
like structure composed of a collection of nerves].
Digestive System
The digestive system starts at the
mouth. Identify each of the bolded
words on the diagram to the right.
Find the mouth opening, the first
part after the mouth is the pharynx,
you will see stringy things attached to
either side of the pharynx (pharyngeal
muscles). The esophagus leads from
the pharynx through the body digestive
system. After the esophagus is a
pocket called the crop, which is
followed by another pocket called the
gizzard. The gizzard leads to the
intestine which is as long as the worm
and ends at the anus, where food is
expelled.
Organ systems [all classes]
Use your book [pg ______ - find it!] to help you.
For the picture below, color code the organ systems for the earthworm using the following key:
Circulatory System – Red
Digestive System – Green
Reproductive System – Blue
Nervous System – Yellow