De rivierkreeft Austropotamobius torrentium in Nederland gevangen in 1956 (Crustacea: Decapoda: Astacidae).

The freshwater crayfish Austropotamobius torrentium collected in the Netherlands in 1956 (Crustacea: Decapoda: Astacidae) On 10 November 1956 a freshwater crayfish was collected in a fish trap in the canal that surrounds the polder Haarlemmermeer between Haarlem and Amsterdam about 2 to 3 km from the village Halfweg. The specimen is a fully grown male of 106 mm in total length; the left first cheliped is missing and the right first cheliped evidently has been lost previously, as a small regenerated cheliped (total length of cheliped 40 mm, length of chela 16 mm) is present. At that time Astacus astacus was the only freshwater crayfish in the Netherlands and the specimen was (incorrectly) identified as that species. As such it was also reported in Geelen’s (1978) discussion of the then known occurrence of freshwater crayfish in the Netherlands. The locality of the specimen was far outside the known Dutch region of occurrence of A. astacus. A recent re-examination of the specimen showed it not to be Astacus astacus, but Austropotamobius torrentium, which made the mystery of its locality only greater. Austropotamobius species have never been found in or near the Netherlands. Moreover, the habitat in which our specimen was found is so completely different from that in which that species usually lives, that its occurrence near Halfweg can only be artificial. How the specimen arrived there will always remain a puzzle. As the species is not a common aquarium animal, the aquarium trade is not likely to be the culprit.