The marbled crayfish or (Procambarus virginalis) is a parthenogenetic crayfish that was discovered in the pet trade in Germany in 1995. Marbled crayfish are closely related to the "slough crayfish", Procambarus fallax, which is widely distributed across Florida. No natural populations of marbled crayfish are known. Information provided by one of the original pet traders as to where the marbled crayfish originated was deemed "totally confusing and unreliable". The informal name Marmorkrebs is German for "marbled crayfish". Model organism Marbled crayfish were the first known decapod crustaceans to reproduce by parthenogenesis. All individuals are female, and the offspring are genetically identical to the parent. Marbled crayfish are triploid animals with 276 chromosomes, which may be the main reason for their parthenogenetic reproduction. It is hypothesized that marbled crayfish originated from an error in meiosis resulting in a diploid gamete, which was then fertilized and created a viable triploid individual in a single generation. Marbled crayfish are thus a model for the rapid generation of species. Unlike other parthenogenetic organisms, the marbled crayfish is a relatively young species; it was discovered in 1995. Because marbled crayfish are genetically identical, easy to care for, and reproduce at high rates, they are a potential model organism, particularly for studying development. A major drawback, however, is the long generation time (several months) compared to other research organisms. The marbled crayfish genome was sequenced in 2018, which provides an essential foundation for further research. Invasive species Marbled crayfish have caused concern as a potential invasive species because only a single individual is needed to establish a new population, and they can reproduce at high rates. Marbled crayfish are also a known carrier of a crayfish plague pathogen, Aphanomyces astaci. Marbled crayfish inhabit freshwater environments, and have not successfully invaded ecosystems with higher salinity levels due to their reduced ability to reproduce and grow. However, it has been proven that they can adjust to increasing saline environments, which may allow for their further expansion. They have since been introduced into natural ecosystems on four continents. They have been found in the wild in the following countries: Austria Belgium China Croatia Czech Republic Denmark Estonia France Germany Hungary Israel Italy Japan Madagascar Malta Netherlands Poland Romania Slovakia Sweden Taiwan Ukraine While initial reports of marbled crayfish in the wild in Europe consisted of only single individuals, the number of European countries reporting populations of marbled crayfish is