Class Oligochaeta
(earthworms)
Major Attributes:
- Hermaphroditic.
- Terrestrial or freshwater habitats.
- Segmented body.
- Specialization in structure of alimentary system.
- Specialization in structure of reproductive system.
Description:
The oligochaetes consist of two main groups, the
megadriles and the microdriles. The megadriles are often known as
earthworms and the microdriles are predominantly aquatic. The body of
an oligochaete may have 100 to 175 segments.
The mouth is on the first segment and the anus is on the
last. Oligochaetes have no eyes, however they do have light-sensitive
organs that are concentrated close to both ends of their bodies.
Touch-sensitive organs are also found in these locations.
Some Interesting Facts:
- When oligochaetes mate, their anterior ends face in opposite directions. Their ventral surfaces touch. Sperm cells are
released by both oligochaetes and held to each organism's body by a
mucus cocoon. Egg cells are
released into the mucus and fertilization occurs. The oligochaete
sheds the mucous 'package' and new oligochaetes form.
- Oligochaetes aerate soil by eating their way through it. Organic
materials are sucked into the alimentary canal by the contraction of
strong pharynx muscles. One part of this canal, the gizzard, has a
great concentration of muscles. This is where most of the soil is
ground up to get available organic material.
Lab Directions:
Specimens available are the common earthworm Lumbricus
terrestris. There are cross-sectional slides and whole preserved.
Make detailed drawings of different regions of the animal's body. Can you
tell what the structure of the internal body is by just looking at the
outside of the animal? Examine the cross-sectional slides closely. What
different organ systems do you see in these slides?
Some Pertinent Books
Found in Lamson Library:
- Brinkhurst & Jamieson. 1973. Aquatic Oligochaeta of the World. Toronto: University of Toronto Press.
- Dales, R. P. 1967. Annelids. London: Hutchinson
University Library.
- Laverack, M. S. 1963. The Physiology of Earthworms. New York: Macmillan.
(Amanda D. Fisher)