Synopsis The present revised and second edition of the book has been carefully organised and clearly written to help advance students and other engaged in teaching. The subject matter has been presented in a step by step systematic manner with clear understandable illustrations. It deals with the morphology, anatomy, physiology and embryology of Balanoglossus, Herdmania and Amphioxus. Special emphasized chapters are Hemichordata: characters& classification; Subphylum Urochordata: characters and classification; Amphioxus (branchiostoma); Salpa; Doliolum; Rhabdopleura; Cephalodiscus; Pterobranchia and its affinities; Asexual reproduction in tunicate; Endocrine glands of the Protochordata etc. Efforts have been made to avoid overburdening the students with information. Many of the omissions are intentional to make the text selective.