Ice worm
Mesenchytraeus solifugus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Annelida
Class:	Clitellata
Order:	Tubificida
Family:	Enchytraeidae
Genus:	Mesenchytraeus Eisen, 1878[1]
Type species
Mesenchytraeus primaevus Eisen, 1878
Species
See text

Ice worms (also written as ice-worms or iceworms, or also called glacial or glacier worms) 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,^[2][3] 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,^[4] and some of the few metazoans to complete their entire life cycle at conditions below 0 °C (32 °F).^[5]

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).^[6][7][8]

Ice worms eat snow algae and bacteria.^[9] 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.^[10]

History

In North America, the first ice worms species were discovered in 1887 in Alaska, on the Muir Glacier. These glacier ice worms can be found on glaciers in Alaska, Washington, Oregon and British Columbia. They have not been found in other glaciated regions of the world.^{[citation needed]}

Description

The specific name solifugus for the North American species, Mesenchytraeus solifugus, is Latin for "sun-avoiding," as ice worms retreat underneath the ice before dawn. Enzymes in ice worms have very low optimal temperatures, and can be denatured at even a few degrees above 0 °C (32 °F). When ice worms are exposed to temperatures as modest as 5 °C (41 °F), their membrane structures disassociate and fall apart (i.e., "melt") causing the worm itself to "liquefy." Ice worms are several centimeters long, and can be black, blue, or white. They come to the surface of the glaciers in the evening and morning. On Suiattle Glacier in the North Cascades, population counts indicated over 7 billion ice worms.^{[citation needed]}

It is not known how ice worms tunnel through the ice. Some scientists believe they travel through microscopic fissures in ice sheets, while others believe they secrete some chemical which can melt ice by lowering its freezing point, like an antifreeze. They feed on snow algae.^[9]

Species

The genus contains 77 species. They are the following:^[6][7][11]

Mesenchytraeus franzi is a junior synonym of Cognettia clarae.^[6] Mesenchytraeus megachaetae Shen, Chen & Xie, 2011 has been renamed Mesenchytraeus gigachaetus Xie, 2012 due to the previous name being preoccupied by Mesenchytraeus megachaetae Bretscher, 1901, a junior synonym of Mesenchytraeus armatus.^[7][12]