About a decade ago a crayfi sh with a hitherto unknown biology was introduced to science, the Marmorkrebs or marbled crayfi sh (Scholtz et al. 2003). This freshwater crayfi sh was only known from aquaria and showed-for the fi rst time among decapod crustaceans-a parthenogenetic reproduction mode. Before 2003 there were rumors in amateur aquarium enthusiasts’ online discussion groups about an enigmatic crayfi sh species of unclear origin which was fi rst sold by an aquarium shop in southern Germany since the mid-1990s (Luckhaup 2001, 2003, Vogt et al. 2004). This crayfi sh, with a beautifully marbled carapace, showed reproduction in the absence of males (Fig. 1.1). These hobbyists noticed that some time after buying a single female the tanks were then full of little crayfi sh. Accordingly, they discussed a variety of possibilities such as sperm storage, hermaphroditism and parthenogenesis to explain this observation. Likewise, discussions about the geographic origin and the systematic affi nities of the marbled crayfi sh led to bewildering speculations.