The present title is a comprehensive uptodate work on the theme, an indispensable text meeting complete requirement of undergraduate and post-graduate students of Zoology. It has been designed to approach the morphology, anatomy, physiology and development of selected type in a very simple and lucid style. In the description of animal types special emphasis has been laid on the functioning of various parts/tissues of the body. General characters and classification nave also been dealt with complete authentic and uptodate account. Separate chapters on topics of significance and general interest pertaining to the phylum have been also added to make the treatment more elaborate. It has been the constant endeavour of the authors to furnish maximum substance, keeping in view the limitations of size of the volume. Ft fort have been made to condense the matter as far as practicable. It is hoped that this title will not only meet the requirement of Indian students but will also be useful as a guideline to the teachers in their teaching.