Question

Problem 2:

a. What is the evolutionary advantage of having a segmented body (metamerism)? Which of the worm

phyla: Plathymelminthes, Nemertea, Nematoda and Anellida has members that have segmented bodies?

b. Mention the differences between the digestive and excretory systems of animals belonging to the phyla mentioned in question a.

Answer 1

a. 1. Segmented body is the part of evolution it is very helpful for locomotion in some order of animals as it helps to move efficiently.As the muscles associated with locomotion can contract and relax with periodicity.

2. The Platyhelminthis species consists of unsegmented soft and bilaterian body. Example : Flatworm. So this option is incorrect.

The Nemertea species have cylindrical shaped or flattened shaped unsegmented body.Example:Ribbon worm.So this option is incorrect.

The Nematoda have bilateral & cylindrical shaped or eel shaped body structure.Example: Hookworm. So this option is incorrect.

The Annelida consists of segmented like body structure.Example: Earthworm.So this option is correct.

The Annelida have segmented bodies.

b. The digestive & Excratory system of diffent phyla:

• Platyhelminthis have incomplete digestive system it consists of- Mouth and Anus,Intestestine.This whole organization is known as the gastrovascular cavity.

It does not have any specialized excreatory organ or system the waste materials are expelled out through the body openings and nearby flame cells.

• Nemertea consits of complete digestive tract one single path from mouth to the anus.

It have specialized organ called Protonephridia and flame cells for excreation of the nitrogenous waste products.

• Nematoda also have comple digestive system and it cosists of- Mouth,Pharynx,Stomach,Intestine,Rectum & Anus.

It have specialized excreatory organ known as-Renette gland.

• Annelida: The digestive system of the annelida ia like a tube it consists of- Mouth, Pharynx, Esophagus, Stomach, Intestine & Anus.

The excretory system comprises of a tubular organ which is known as Nephridia.