The llyocryptidae Smimov, 1971 emend Smimov, 1992 (Branchiopoda: Cladocera: Anomopoda), with the single genus llyocryptus Sars, 1862, are a compact, highly specialized group of Anomopoda (Crustacea: Branchiopoda), currently including 46 formal taxa at the species-group level, published and available according to the ICZN (2000). The main problem confronting an investigator of llyocryptus is, frequently, the limited material available for study. From the beginning to the middle of the 20th century, all interest in the systematics of the genus llyocryptus was lost. Only after publication of the book by Smimov (1976), did it become clear that the diversity of ilyocryptids had been greatly underestimated.
This book is therefore an attempt to summarize available data on the systematics and distribution of all currently known species of the genus. In particular, the authors here propose a key for species identification to hydrobiologists interested in tuming their attention from the simplified planktonic communities to the more complex and species-rich littoral.