Question

Using the tree you drew, give an example of sequential evolution of a defining character. Why might this character have evolved?

Answens -Porifera cnidana Animal Platyhelminthy mollweg Arthropoda Echinodermeta -Chordata - By this hypothefized clado grom we com say that chordata iq most advance and Porifera is less developed cordoeta have most of the charoter in common and Porifena hawe Jeast common character. I

Answer 1

An exmaple of sequential evolution of a defining character is the symmetry of the animals.

There are three types of symmetry that is being studied-

• asymmetrical

• radial

• bilateral symmetry

Porifera is the animal kingdom in which animals like sponges do not show any symmetry and they appear as asymmetrical. There body plan is not well defined. During course of time, the animals evolved a central axis around which they studded their top and bottom , but still there were no clwar right or left being distinguished properly .The body is arranged like rays around the axis in animals like cnidarias and ctenophora show radial symmetry. This type of symmetry is known as radila symmetry. The body of these animals having radial symmetry can be divided into two halves. As the animals evolve further,the symmetry also changed . This causes division of animals resulting into two mirror images , causing right and left halves. It is divided into only one plane. They have head as well as foot with differentiable right and left halves. As in echinodermata, the adults are radial symmetrical while larval stages are bilateral symmetrical. The symmetry in adults is derived from bilateral symmetry and is known as secondary radial symmetry. This character has evolved during course of time because body arrangement from animals with lower phyla to higher phyla shows tmthe evolutionary advancement towards increasing complexity and proceeding development of more well defined body plan.

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