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.

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.

Protastacus would have lived alongside various fish, invertebrates and aquatic reptiles in this lake, while terrestrial animals such as dinosaurs inhabited the surrounding shores.

[1] Later in 1905, Erich Harbort studies fossilized remains in clay ironstone geodes found north of Bückeberg, Germany and erects the species Astacus antiquus based on them.

[6][7] In 2003, Rode and Babcock found that Protastacus belonged to the family Astacidae, making Protastacidae an invalid grouping.

[12] Protastacus is believed to be a brackish water animal, as analysis of hydrogen, carbon and sulphur ratios as well as the presence of Botryococcus algae in the Bückeberg Formation prove the depositional environment was brackish-freshwater.

[13] The Bückeberg Formation likely represented a large lake receiving fluvial drainage from the surrounding uplands and connected to the Boreal Sea to the west by narrow passage.

[14][15] Fossil remains of various aquatic animals have been found here which would have lived alongside Protastacus, such as molluscs, crustaceans, fish (hybodonts, Indaginilepis and Scheenstia), turtles (including Hylaeochelys, Pleurosternon and Dorsetochelys (=Ballerstedtia)[16]), the plesiosaur Brancasaurus, and crocodyliforms (Goniopholis and Pholidosaurus).