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Representatives of the genus Simocephalus Schoedler, 1858, or 'tailless water fleas', are rather large (up to 3.5 mm), non-pelagic Daphniidae. They are abundant in the littoral one and in submerged aquatic vegetation in freshwater bodies of smallest to largest sizes all over the world. These animals are often the dominant species of littoral commmunities. Exceptionally, in lakes without pelagic fish, some species may become pelagic (e.g. in Lake Naivasha, Kenya, H. Dumont, pers.com.). Several among them are widely used as models in toxicologic, ecological, physiological, and other investigations. They also have some economic significance, because they are used as prey by the fry of numerous commercial fish species. Thus, a proper identification of these anomopods is necessary for many purposes.
Cladocera: Anomopoda is the result of a seven-year study. It summarizes data on morphology and taxonomy of Simocephalus obtained earlier (Orlova-Bienkowskaja 1993a, 1993b, 1995a, 1995b, 1998). The key is based on a thorough revision and includes all taxa published to date: 63 specific and subspecific names have been proposed before, 20 of which are regarded as valid names here. For each species a differential diagnosis and accounts of its nomenclature, distribution, and morphology are given. All species except one are illustrated based on original figures. Besides, the key is supplied with figures, specifically designed to facilitate the process of identification. The numbers of these figures correspond to the numbers of the couplets in the key.
The author paid special attention to a description of intraspecific variability. It is importantant to distinguish this from interspecific differences. For example, S. serrulatus was described by different authors under a different name about 15 times, because of its strong morphological variability.
In addition to identification of known species, the present key may be useful for recognising as yet undescribed taxa. A detailed account of morphology given in the beginning of this book. It should facilitate the process of recognizing any new taxa prior to description. Probably, several American species of Simocephalus have not been discovered yet; this region has definitely remained underinvestigated to date. It is therefore not surprising that a species belonging to the S. (acutirostratus) group from North America was recently identified by B. Hann.