In this Special Issue, we address the state of the art of the systematics of the main annelid groups and the improvements in the diversity they hold, with special emphasis on the latest discoveries in well-studied areas, expeditions to unsurveyed areas or environments, or the use of novel techniques that allow for the improvement of biodiversity knowledge. We are hoping that this Special Issue will provide a platform facilitating a review of current knowledge on the subject, identifying current research problems, as well as indicating directions and research trends for the future.

Annelids (the segmented worms) exist in a remarkably diverse range of mostly marine but also freshwater and terrestrial habitats, varying greatly in size and form. This text provides. This text begins with an introduction to the phylum and an outline of annelid taxonomy. The book describes their collection and the methods to ensure their optimal preservation, and provides an overview of anatomy with its relevant terminology. It includes the latest molecular phylogenomic evidence and is organised based on a new, robust phylogenetic hypothesis. It looks at groups which include Clitellata (comprising more than a third of total annelid diversity), Sipuncula, and Thalassematidae (formerly Echiura). It reflects the enormous amount of research on these organisms that has burgeoned since the millennium, principally due to their use as model organisms to address wider and more general evolutionary and ecological questions.

This reference work is designed to provide background information on an array of northeastern Pacific marine invertebrate species so that they can be more easily included in comparative studies of morphology, cell biology, reproduction, embryology, larval biology, and ecology. It is meant to serve biologists who are new to the field as well as experienced investigators who may not be familiar with the invertebrate fauna of the northern Pacific Coast. The species discussed in this volume are mostly from the cold temperate waters of the San Juan Archipelago, near Puget SOund and the Strait of Georgia, but the information and methods given will be useful in laboratories from Alaska to central California and applicable to some extend in other coastal or inland facilities. An introductory chapter discusses basic prodcedures for collecting and maintaining mature specimens, for initiating spawning, and for culturing embryos and larvae in the laboratory. Subsequent chapters summarize reproduction and development in thirty different invertebrate groups and provided ercent references through which additional information can be traced, cite monographs or keys needed to identify species, and give methods useful for studying an array of selected species. Available information on habitat, diet, reproductive mode, egg size, developmental pattern, developmental times, larval type, and conditions for settlement and metamorphosis is reported for over 450 species.

Embryology and Phylogeny in Annelids and Arthropods describes the embryology of segmented invertebrates, utilizing morphological facts of embryonic development in the furtherance of speculations on phylogenetic relationships. This book begins with an introduction to embryology and phylogeny, followed by a discussion on the experimental embryology of animals groups, such as polychaetes, oligochaetes and leeches, onychophorans, myriapods, apterygote and pterygote insects, crustaceans, and chelicerates. The cleavage, gastrulation, and basic pattern of development of these invertebrates are also provided. This text concludes with a presentation of the onychophoran-myriapod-hexapod assemblage or Uniramia. This publication is recommended for experimental embryologists researching on the embryonic development in annelids and arthropods.