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.

A comprehensive account of Polychaetes in Australia. Based on nearly 2400 references, the authors reveal the wealth of diversity in the largely unknown world of these worm groups, in terms of their morphology, behaviour, reproduction and significance in marine ecosystems.

This book is the fourth in a series of 4 volumes in the Handbook of Zoology series about morphology, anatomy, reproduction, development, ecology, phylogeny and systematics of Annelida. It covers the most typical polychaetes, Phyllodocida, together with certain smaller taxa placed incertae sedis. This volume completes the polychaetous Annelida. Phyllodocida are often vagile, possess well-developed parapodia. Due to their broad and flat cirri these parapodia look like leaves in some taxa and leading to the name of the entire group. Many of its members are macrophagous and often predators. Accordingly most species possess elaborate sense structures such as sensory palps, antennae, eyes and nuchal organs. In certain species the eyes comprise thousands of photoreceptor cells and lenses most likely allowing forming true images. Phyllodocida typically possess an axial muscular pharynx called proboscis functioning as a kind of suction pipe allowing them to swallow and ingest their prey or other food. This pharynx may be armed with cuticular jaws and some species even possess venom glands. The probably most popular and important polychaete model organism, Platynereis dumerilii, belongs to this interesting group. Phyllodocida fall into two to three higher clades comprising about 25 families which represent more than one fourth of the polychaete diversity. One of these families, Syllidae, comprises about 700 valid species of mainly small size and may, therefore, represent one of the most complex and somehow difficult polychaete families on Earth.