Mammoth Spring Crayfish

Orconectes marchandi
Cambaridae (freshwater crayfish) in the order Decapoda (shrimp, crabs, and lobsters)

This is a reddish-brown crayfish with broad, powerful pincers. The pincers have numerous blackish specks on their basal parts. The abdomen is dark rust-red without specks. The carapace is light tan, with a dark brown band crossing the back of the head and another at the junction of the carapace and abdomen. This crayfish bears a striking resemblance to the Ozark crayfish, and both species occur in the Warm Fork. Males of the two species are easily distinguished by the shape of the reproductive structures (gonopods). The gonopod tips are long and slender in the Ozark crayfish, short and blunt in the Mammoth Spring crayfish. The Ozark crayfish is lighter tan and less reddish, especially on the pincers.

Adult length: about 1 1/2 to 2 1/2 inches.
Habitat and conservation: 
The Warm Fork of the Spring River, where it is found in our state, is a medium-sized, clear Ozark stream with well-defined riffles and runs. This species occurs on riffles over gravel or rubble substrate.
Distribution in Missouri: 
The Mammoth Spring crayfish has a very localized distribution near Mammoth Spring in the Spring River of Arkansas and Missouri. In our state it has been collected only from Warm Fork (and two of its tributaries) of Spring River near Thayer.
This may be Missouri’s rarest crayfish.
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