Signal crayfish was created in 1852.
I have caught signal crayfish in the river flit, where it runs through Shefford.
Murray crayfish was created in 1866.
Rusty crayfish was created in 1852.
Tasmanian giant freshwater crayfish was created in 1936.
Three species of crayfish are present in Finland, Astacus astacus (Noble grayfish), Astacus leptodactylus (Danube crayfish) and Pacifastacus leniusculus (Signal crayfish), for your question about 'Why?', I can't answer anything else than the climate and water conditions are suitable for these species of crayfish.
Threat Signal was created in 2003.
No Signal was created on 2001-10-09.
A Signal Shattered was created in 1999.
Signal Morning was created in 2009.
Tideland Signal was created in 1954.
Warsaw Signal was created in 1841.
The Signal-Man was created in 1866.