LABORATORY 6

PHYLUM  ANNELIDA

PHYLUM ARTHRPODA

OBJECTIVES OF THE LABORATORY

1.         To examine the basic body plan, and the feeding, respiratory, circulatory, excretory and reproductive systems of the Phylum Annelida.

2.         To examine the basic body plan, and the feeding, respiratory, circulatory, excretory and reproductive systems of the Phylum Arthropoda.

I           PHYLUM ANNELIDA

Annelids include a variety of marine, freshwater, and terrestrial worms including the familiar leeches and earthworms. The most distinctive feature of the members of the phylum Annelida is the division of their bodies into rings or segments (Latin annellus = little ring).  This type of body segmentation is called metamerism.  In the annelids, metamerism is evident in the external features of the worms, which accounts for their common name, the segmented worms.  As well, most annelids also show internal metamerism with the division of the body into compartments by regularly repeated septa (walls) and by the repetitive arrangement of organs and organ systems.  Annelids show several evolutionary advances over the phyla that you have studied so far.  They have a true coelom, fully lined with a layer of mesodermal epithelium, the peritoneum; a more centralized nervous system and a closed circulatory system.  Most annelids also have setae, which are small, bristle-like appendages.  

            The Phylum Annelida is subdivided into four classes: Oligochaeta, Polychaeta, Hirudinea, and Archiannelida.  Observe the specimen jars on display for the first three classes and note their characteristic segmentation.

Class: Oligochaeta  - Lumbricus terrestris

  Class: Polychaeta - Fan worms

Tubeworms from the deep ocean vent communities.

Another polychaete worm.

Class: Hirudinea - a leach.

We will study the body plan, digestive, excretory, respiratory, circulatory and reproductive systems of the earthworm Lumbricus terrestris (a common oligochaete), and the marine clamworm Nereis sp. (a polychaete).