1) Arthropod genus 2) Genus astacus 3) Offspring of Hermes 
Astacus (from the Greek αστακός, astacós, meaning `lobster` or `crayfish`) is a genus of crayfish found in Europe and western Asia, comprising three extant and four extinct species. Due to the American crayfish plague, crayfish of this genus have been almost wiped out in Europe and have in many European countries been replaced by the N...
As'ta·cus noun [ Latin astacus a crab, Greek ....] (Zoology) A genus of crustaceans, containing the crawfish of fresh-water lobster of Europe, and allied species of western North America. See Crawfish . 
[n] - type genus of the family Astacidae
genus Astacus noun type genus of the family Astacidae; Old World crayfish