This book has been designed both as a guide to the identification of the common and widespread organisms of the shore and as a biological text giving information on their biology and ecology. It is intended for use by students, lecturers and teachers, and also by naturalists and others who might have little or no formal scientific training.

In the following pages, the different groups of organisms are arranged in phylogenetic sequence. Readers who are unable initially to assign an organism to its phylum or group are referred to the illustrated guide on p. 11. When the phylum or group to which an organism belongs is known, reference can be made directly to the appropriate chapter where the reader will find an introduction giving the main characters of the phylum or group together with a full classification in which those classes, subclasses, orders, etc. included in this text are highlighted in bold type. A brief statement on the morphology and biology of the group is also included. For most groups a simple dichotomous key is provided. In some cases this is to the level of families and leads to a full statement of family characteristics, followed where appropriate by a key to species. In other cases the phylum or group has been keyed directly to species. Morphological features are the basis on which identification is made but in many cases the type of substratum on which the organism is found, position on the shore and distribution are important characteristics.