Faxonius immunis, (Hagen, 1870)
Faxonius immunis is a species of crayfish in the family Cambaridae. It is native to North America and it is an introduced species in Europe, where it lives along the Upper Rhine. Its common names include calico crayfish and papershell crayfish.
Faxonius immunis is similar to a number of species of crayfish in the genus Faxonius. While the colouration of the claws is distinctive, it can be difficult to use that to identify a specimen without reference specimens for comparison. F. immunis can be distinguished from F. virilis by the presence of a notch near the base of the dactylus (finger) of the claw, which is not found in F. virilis.
Faxonius immunis naturally occurs across a wide area of eastern North America, from Maine and Connecticut in the east to Colorado and Wyoming in the west, and from Alabama in the south and north to Manitoba, Ontario and Quebec in Canada. Populations in Quebec may be the result of introductions by anglers from New York; the Canadian populations are centered in southern Ontario. It is believed to have been introduced to a number of states in New England, including Massachusetts, Maine, New Hampshire, Rhode Island and Vermont.
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