Tags: Crustacean.
Pacifastacus nigrescens the sooty crayfish was a species of crayfish in the family Astacidae. It was originally described in 1857 by William Stimpson from the area around San Francisco where it was once common in the creeks surrounding San Francisco Bay. The signal crayfish Pacifastacus leniusculus was introduced to California probably in the 19th century and since then there have been no sightings of P. nigrescens which is now believed to be extinct.