Although the students can “Annelids” on the Tree of Life, this is a good time to point out that there are many phyla that are missing. There are many worm-like organisms but not all of them belong to the familiar earthworm group. Students will learn of 2 other worm-like phyla. Although students are familiar with the earthworm, and view them as harmless, students should become aware of "worms" that can be harmful.
Nematoda, called roundworms are found in the sea, fresh water, and in
soil. They occur from the polar
regions to the tropics including deserts, hot springs, high mountains, and
great ocean depths. An acre
of good farm soil contain several hundred million to billions of terrestrial
nematodes. A single decomposing
apple can house 90,000 nematodes. They
can be either free living or parasitic.
The free living especially freshwater and terrestrial forms are less
than 1 mm. Nematodes are
relatively perfect cylindrical shape and has a radical arrangement of
structures around the mouth. The
parasitic nematodes attack virtually all groups of animals and plants.
Hookworm and trichinosis are parasites that causes serious infections
The flatworms or Platyhelminthese includes flukes, tapeworms which are
parasitic and free living forms including planarian.
Planaria belong to a group called Turbellaria. Their shape varies from ovoid to elongate, and are dorso-ventrally
flattened. Head projections are
present in some species. They
range in size from 60 cm long although some are 10 mm in length.
They are primarily aquatic, with the majority marine.
They live in the bottom within the sand or mud.
Freshwater forms include the planarian, which live in lakes, ponds,
streams, and springs. Some of the
larger planaria living in a terrestrial environment confined to very humid
2. 10-20 mm
Lives in bottom of sand or mud in lakes, rivers, ponds
Some live in very humid areas on land
live in all environments
Can be free living or parasitic
Head area (anterior) has spine-like structures
3 classes marine worms, earthworms, and leeches
many are hermaphroditic (male/female)
segmentation is highly developed
locomotion by peristaltic contractions
scavengers, feed on dead vegetable matter