Lesson 1 - Page 1




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 in humans.

            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 areas. 

            The annelids are composed of 3 classes including the Polychaeta (marine worms), oligochaeta (earthworms) and Hirudinea (leeches).Students will be looking at Lumbricus which is an oligochaeta.  Below is a figure of the dorsal view of the anterior internal structure of Lumbrius.  However, when students dissect their earthworm they may not see this.  This is a good time to explain why we look at thin sections of organisms.  The reproduction of earthworms is interesting.  Introduce the term hermaphroditic, which means that individuals posses a male and female part.  (However, they can not made with themselves).    The ovaries and testes, both of which are paired, are situated in the lower part of the anterior septum.





2. 10-20 mm

3.  free living

4.  Lives in bottom of sand or mud in lakes, rivers, ponds

5.  Some live in very humid areas on land



1.  Roundworms

2.  live in all environments

3.  Can be free living or parasitic

4.  Head area (anterior) has spine-like structures



1.  3 classes marine worms, earthworms, and leeches

2.  many are hermaphroditic (male/female)

3.  segmentation is highly developed

4.  locomotion by peristaltic contractions

5.  scavengers, feed on dead vegetable matter

6.  straight gut

7.  great powers of regeneration




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