| Protastacus Temporal range:
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| Illustration of a P. politus fossil | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Malacostraca |
| Order: | Decapoda |
| Suborder: | Pleocyemata |
| Infraorder: | Astacidea |
| Superfamily: | †Protastacoidea Albrecht, 1983 |
| Family: | †Protastacidae Albrecht, 1983 |
| Genus: | †Protastacus Albrecht, 1983 |
| Type species | |
| †Astacus politus Schlüter, 1868
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| Species | |
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| Synonyms | |
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P. antiquus synonymy:
P. politus synonymy:
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Protastacus is an extinct genus of decapod crustaceans that lived in what is now Germany during the early Cretaceous period. The type species is P. politus, and a second species, P. antiquus, is also assigned to the genus. Protastacus grew to around 10 cm (3.9 in) long and had a mostly crayfish-like appearance, with enlarged pincer-bearing appendages and a segmented abdomen. Though formerly assigned to the Astacidae or Nephropoidea, it is currently placed as the only genus in the family Protastacidae, which in turn is the only family in the superfamily Protastacoidea.
Both known species are believed to be brackish water animals, inhabiting a large upland-surrounded lake where the Bückeberg Formation was deposited during the earliest Cretaceous. This lake was originally freshwater and connected to the Boreal Sea, but became brackish due to marine transgression. Protastacus would have lived alongside various fish, invertebrates and aquatic reptiles in this lake, while terrestrial animals such as dinosaurs inhabited the surrounding shores.