Introduction
No one can deny the importance of taxonomy in the field of science. One of its major goals is to identify species that inhabit a certain habitat.
Zooplankton refers to the weak swimming animals or those which move under the mercy of water current. They occupy a central position in the food chain in the aquatic ecosystems between primary producers and higher consumers. Zooplankton plays an important role in a lake’s ecosystem and food chain. Unlike algae, or phytoplankton, zooplanktons are microscopic animals that do not produce their own food. They are responsible for eating millions of little algae that may otherwise grow to an out-of control state. Through their consumption and processing of phytoplankton and other food sources, zooplankton plays a role in aquatic food webs, as a resource for consumers on higher trophic levels (including fish), and as a conduit for packaging the organic material in the biological pump. Since they are typically small, zooplankton can respond rapidly to increases in phytoplankton abundance for instance, during the spring bloom.
The present book is an attempt to identify the common species of zooplankton inhabiting north-west region of Saudi Arabia (Tabuk). The species recorded in the book were collected by the authors through a project funded by Tabuk University in 2014 (project No. 0151-1434-S). The sites of collection included 76 sites covered the region. The sites included a variety of habitat that covered temporary and permanent ponds, streams, wells, reservoirs, and hot springs. Some specimens were identified till species level but others could not be identified due to that they were larvae or immature stages which make the task very difficult. The book is considered as a preliminary guide to identify common zooplankton inhabiting inland waters of Tabuk region and other regions of Saudi Arabia. The need for such a book arises from the fact that few previous attempts were made to record zooplankton in the region. In addition that the region can be considered as a unique habitat in its characteristics as an arid habitat. The nature of the habitat is mainly desert, so it is not easy to reach the areas of collecting without a guide and the majority of sites were temporary lakes or ponds. So, the authors of the book hope that this work will initiate future works in this field in Tabuk and other regions of the Kingdom of Saudi Arabia to cover the whole region. It was found better and more beneficial to add some information about the collected taxa from different references published around the world. The book includes the following main topics: an overview on zooplankton, the investigated sites for collecting zooplankton at Tabuk region, review on zooplankton of Saudi Arabia, List of zooplankton recorded at Tabuk region, description of the common species and the references.
The authors hope that the guide will help the taxonomists to identify common zooplankton taxa inhabiting inland water of Tabuk region and other regions in the Kingdom of Saudi Arabia. Consequently, we hope that this identification of the taxa will initiate further studies on this important group of animals.

The authors