Cambarus
Cambarus is a large and diverse genus of crayfish from the United States and Canada. The adults range in size from about 5 centimeters (2 in) up to approximately 15 centimeters (6 in). Description. The genus "Cambarus" is the second largest freshwater crayfish genus inhabiting the Northern Hemisphere, with only sixty fewer species than the genus "Procambarus". Though "Cambarus" are varied across species, the two terminal elements that make up the male form I gonopod form ninety degree angles with the central appendage, allowing for their identification. Unlike the genus "Procambarus" whose first pleopod tends to have three processes  at the tip, "Cambarus" has only one or two. "Cambarus" reach 17–26 mm carapace lengths in their first year, while average adult carapace length ranges from 55–62 mm. As a genus containing nearly 100 species, "Cambarus's" coloration is variable. "Cambarus bartonii" is dark brown, while species like "Cambarus pauleyi" range from subtle to vibrant blues and reds. Other species are light green or grayish in color. Biogeography. Most species of "Cambarus" are restricted to the United States and Canada. They are distributed along the eastern coast, extending from New Brunswick to northern Florida. However, the genus extends as far  westward as the Rocky Mountains of Wyoming and Colorado, inhabiting a variety of freshwater environments. Habitat. "Cambarus" occupy a range of freshwater environments including streams, rivers, lakes, and burrows. Burrowing species of the genus include "Cambarus dubius". "Cambarus" also include many cave-dwelling species, both stygobites and stygophiles. While salinity and temperature changes minimally affect "Cambarus", the genus has shown an intolerance to pollution. Ecology. Diet. Like other crayfish, "Cambarus" are foragers. Diets are largely plant-based, though "Cambarus" also consume small marine organisms like molluscs, larvae, tadpoles and amphibian eggs. "Cambarus" consume small rodents or birds when available. In  their first year, "Cambarus" typically consume 1-4% of their overall body-weight each day. The genus is central to many freshwater food webs as they help maintain water quality through consumption of algae. Vulnerability. One of the largest crayfish genera, "Cambarus" includes a sizable number of vulnerable species. Cave-dwellers like "Cambarus jonesi" are at risk due to their lack of genetic diversity and low population count. Other species like "Cambarus veteranus" are at risk due to human practices like logging and mining, which increase sediment amounts in freshwater environments. Increased sediment causes these freshwater environments to be inhabitable , and "Cambarus" are forced to relocate as a result. Behavior. Growth. Molting occurs among "Cambarus" approximately 5-10 times during their first year, and 3-5 times during subsequent years. "Cambarus" remain relatively inactive during periods of molting, as the shedding of chitinous exoskeletons leaves them more vulnerable to predation and injury. Many species of "Cambarus" continue to grow well into adulthood. Reproduction. "Cambarus" typically mate in the early spring. Both "Cambarus bartonii" and "Cambarus robustus" only mate once during their three-year life span, with females of both carrying fewer eggs than those of the genus "Orconectes". Classification. The  genus "Cambarus" contains around 100 species, many of which are listed on the IUCN Red List. Species in the genus were formerly divided among 12 subgenera. In a 2017 study, these subgenera were found to lack any phylogenetic validity and were therefore eliminated.