Ice worms (also written as ice-worms or iceworms) are enchytraeid annelids of the genus Mesenchytraeus. The majority of the species in the genus are abundant in gravel beds or the banks of riverine habitats, but the best-known members of the genus are found in glacial ice. They include the only annelid worms known to spend their entire lives in glacial ice, and some of the few metazoans to complete their entire life cycle at conditions below . They were discovered in a wide range of environments, which include level snowfields, steep avalanche cones, crevasse walls, glacial rivers and pools, and hard glacier ice. These organisms are unique in that they can simply move between tightly packed ice crystals. They utilize setae, which are small bristles found on the outside of their bodies, to grip the ice and pull themselves along. The genus contains 77 species, including the North American glacier ice worm (Mesenchytraeus solifugus) and the Yosemite snow worm (Mesenchytraeus gelidus). Ice worms eat snow algae and bacteria. They live at zero degrees Celsius (32 degrees Fahrenheit), but if temperatures dip even slightly below that, according to a Washington State University researcher, the worms die. Species The genus contains 77 species. They are the following: Mesenchytraeus affinis Michaelsen, 1901 Mesenchytraeus altus Welch, 1917 Mesenchytraeus americanus Bell, 1942 Mesenchytraeus anisodiverticulus Shen, Chen & Xie, 2012 Mesenchytraeus antaeus Rota & Brinkhurst, 2000 Mesenchytraeus arcticus Bell, 1962 Mesenchytraeus argentatus Nurminen, 1973b Mesenchytraeus armatus (Levinsen, 1884) Mesenchytraeus armatus armatus (Levinsen, 1884) Mesenchytraeus armatus kananaskis Dash, 1970 Mesenchytraeus asiaticus Eisen, 1904 Mesenchytraeus atriaphorus Altman, 1936 Mesenchytraeus beringensis Eisen, 1904 Mesenchytraeus beumeri (Michaelsen, 1886b) Mesenchytraeus bungei Michaelsen, 1901 Mesenchytraeus cejkai Cernosvitov, 1937d Mesenchytraeus celticus Southern, 1909 Mesenchytraeus chaunus Piper, MacLean & Christensen, 1982 Mesenchytraeus chromophorus Altman, 1936 Mesenchytraeus crenobius Timm, 1994 Mesenchytraeus diplobulbosus Bell, 1949 Mesenchytraeus diverticulatus Piper, MacLean & Christensen, 1982 Mesenchytraeus eastwoodi Eisen, 1904 Mesenchytraeus eltoni Stephenson, 1925 Mesenchytraeus falciformis Eisen, 1878 Mesenchytraeus flavidus Michaelsen, 1887 Mesenchytraeus flavus (Levinsen, 1884) Mesenchytraeus fontinalis Eisen, 1904 Mesenchytraeus fontinalis fontinalis Eisen, 1904 Mesenchytraeus fontinalis gracilis Eisen, 1904 Mesenchytraeus franciscanus Eisen, 1904 Mesenchytraeus fuscus Eisen, 1904 Mesenchytraeus fuscus fuscus Eisen, 1904 Mesenchytraeus fuscus inermis Eisen, 1904 Mesenchytraeus gaudens Cognetti, 1903a Mesenchytraeus gelidus Welch, 1916 Mesenchytraeus gigachaetus Xie, 2012 Mesenchytraeus glandulosus (Levinsen, 1884) Mesenchytraeus grandis Eisen, 1904 Mesenchytraeus grebnitzkyi Michaelsen, 1901 Mesenchytraeus groenlandicus Nielsen & Christensen, 1959 Mesenchytraeus hamiltoni Healy, 1996b Mesenchytraeus harrimani Eisen, 1904 Mesenchytraeus hydrius Welch, 1919a