Chapter 25, Problem 19A

Summary Introduction

To determine:

The distinguishing character of the flatworm and the roundworm that help in determining the organism is a round worm or a flat worm.

Introduction:

The Platyhelminthes contains different organism that are free and parasitic. They are divided into three classes: turbellaria (flatworm), trematodes, and cestode. Roundworm belong to Nematoda phylum.

Explanation of Solution

The flatworms are worms that have a head and tail. As the name suggests they are flat and bilaterally symmetrical. They do not have body cavity. They are bilaterally symmetrical with a definite upper and lower surface.

The round worms are called so because their body is cylindrical and long, they do not have definite dorsal and ventral surface. They are bilaterally symmetrical. The ends of the worms are tapered or pointy at both ends. They are intestinal parasites and they are not involved in active movements. So, their body lack segmentation. They have pseudocoelom.

Hence, if the organism is flat and unsegmented it would be a flatworm and if it is round and have tapered ends, it would be a round worm.