Chapter 18, Problem 17TYK

Summary Introduction

To compare: The structure of planarian and earthworm with regard to their: digestive tract, body cavity and the segmentation.

Concept introduction: The Planaria is a flatworm that is included in phylum Platyhelminthes. They have no body cavity as they are flat. They resemble ribbon shape and are about 1mm to 20 m. They have incomplete digestive system. They show bilateral symmetry. Many species of flatworms are parasitic in nature. The flatworms are bilaterally symmetrical animals.

The Earthworm is included in phylum Annelida which is the group of animals that are included in the invertebrates. These are the true segmented worms that have flexible body and no hard skeleton is present in their body. They have closed circulatory system, small brain, nervous system and excretory system. They do not have legs. Their body cavity is filled with coelom. Their size range from 1 mm to 3 m. They are found in various habitats like in soil, at the bottom of the ocean or in fresh waters.