Earthworms are invertebrates. That is, they do not
have a backbone. Insects, sea stars, spiders, jellyfish, and
millipedes are other examples of invertebrate animals.
Study the illustration of an earthworm shown below. You
will notice that earthworms have long, cylindrical body that
is divided into similar segments. The grooves that
extend around the body of the worm show the arrangement of
Some species of earthworms have a body composed of over
100 segments. How many segments does your earthworm have?
Earthworms have bilateral symmetry. This means that
if you cut the earthworm down the centerline, the left side
of the body would be identical to the right side.
One of the key features of an earthworm is the colour of
its body. Some species of earthworms have a dark-red
or red-violet body while other species are muddy-green.
However, there are species that do not have these colours.
For the purposes of Worm Watch, these animals are said
to have "other body colours."
Some species of earthworms have a tongue-like lobe above
the mouth called prostomium. The prostomium is actually
a sensory device. Earthworms do not have a nose, eyes, ears,
or hands to gather sensory information about their environment.
Instead, they depend on their prostomium and sensory receptors
in their skin to "feel" their way through the soil.
The first body segment is called the peristomium.
The peristomium contains the mouth.
Adult (sexually mature) earthworms have a distinct swelling
called a clitellum. It is located about one-third of
the way down the earthworm. The clitellum is often white or
orange in colour. It produces most of the material secreted
to form earthworm cocoons. The clitellum forms a band that
can be flared, non-flared, saddle-shaped, or annular. It is
generally found between segments 26 and 33.
The clitellum is only found on adult worms. Young or juvenile
worms do not have a clitellum. The clitellum of each species
of earthworm has a distinct colour, size, and shape. Another
key structure found on the clitellum is the tubercula pubertatis.
The diagram shows the shape and structure of the clitellum.
They may have any combination of shapes.
|Tubercula Pubertatis (TP)
The tubercula pubertatis (TP) is another structure
used to identify earthworms. The TP are glandular swellings
located on both sides of the clitellum. They can assume a
variety of shapes such as long and narrow, triangular, or
The shape and location of the tubercula pubertatis (TP)
on the clitellum are key features used to identify mature
|Genital Tumescences (GT)
The genital tumescences (GT) are areas of modified
epidermis (skin) that do not have distinct boundaries. These
are openings through which follicles of genital setae open.
The pattern and location of the GT are important clues to
identifying different species of earthworms.]
Locate the clitellum of a mature earthworm. The shorter
region to one side of the clitellum is the anterior
or head-end of the animal. This end of the worm is usually
more pointed than the posterior end of the animal.
The prostomium is the first segment at the anterior end
of the animal.
Locate the clitellum of a mature earthworm. The longer region
is the posterior or tail end of the earthworm.
The top-side of an animal is called the dorsal surface.
For example, the fin you see in all shark movies shows the
dorsal fin of a shark just before it attacks. The dorsal surface
of some species of earthworms is darker than its ventral surface.
The bottom-side of an animal is called the ventral
surface. In many animals, the ventral surface is a lighter
colour or shade than the dorsal surface.
The periproct is the last segment of an earthworm.
Each segment, except the first and last, have tiny bristle-like
structures called setae. These structures help the
earthworm to move and act to sense the environment.
The number and arrangement of setae are important clues
to the identification of earthworms.]
The epidermis is the name for the skin of an earthworm.
It is the outer layer of worm and it secretes a mucous.