The present publication has been designed to approach the morphology, anatomy, physiology and development of selected type in a simple and lucid style. Important animal types of the phylum have been dealt and efforts have been made to present their elaborate and up-to-date account. General characters and classification and brief description of other important types of the phylum have also been dealt. The method of presentation is very clear and lucid, which can be easily followed by the students. The content conform to the specified syllabi of several Indian universities and it is our earnest hope that the publication will be of great value to all our students.