North American glacier ice worms on Mount Rainier

''Mesenchytraeus solifugus'', commonly called an

ice worm 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 t ...

, is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

of oligochaete worm that inhabits coastal glaciers in northwestern North America. ''M. solifugus'' is dark brown and grows to about 15 mm long and 0.5 mm wide. It has a high population density and is common in suitable habitat. It can only survive at temperatures of approximately –7 °C to 5 °C. The ice worm is studied for its ability to survive in low temperatures. It has heavy

pigment A pigment is a colored material that is completely or nearly insoluble in water. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compo ...

, absorbing most colors; however, it burrows into the glacier to avoid strong sunlight.

History and taxonomy

This species was first reported from Muir Glacier in Alaska. Carlo Emery named it ''solifugus'' in 1898, meaning "fleeing from the sun". Phylogeny suggests that it evolved from an aquatic ancestor.

Description

Ice worms are the only known psychrophilic annelids. Adult ice worms are approximately long. They live their entire lives in snow or ice. The ice worm’s dark pigmentation helps protect it from solar ultraviolet radiation. Their fluid and flexible body are able to squeeze through air holes and tiny crevasses in ice. Their lifespan is believed to be five to ten years. Ice worms have an elongated head pore, with sensing organs located on their

prostomium The prostomium (From Ancient Greek, meaning "before the mouth"; plural: prostomia; sometimes also called the "acron") is the cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does not include) th ...

and ventral surface. These organs are responsible for chemo-, thermo, and photorecepetion. However, the worms lack eyes or eyespots. They have setae that curve at the tips, unlike those of related organisms. Little is known about the life cycle of the ice worm; it is thought to be unusually slow. It requires temperatures of 0 °C for a successful reproduction. Cocoons are dispersed by birds. Not much is known about the ice worm's diet, but it is thought to eat snow algae, as well as some bacteria.

Habitat

Ice worms inhabit glaciers and can be found in snowfields, avalanche cones, and glacier rivers and pools. These environments have temperatures near the freezing point and are nutrient poor. The organisms require permanent glacial environments for survival and reproduction. As well as the northwestern United States, ice worms have been found in glaciers of southern Alaska and certain parts of British Columbia. They can be abundant, with typical densities of about 100 per square meter and peak recorded densities of up to 6,000 per square meter. Though they are found in snowfields, rivers and pools, they are not found on dirty snow or rock.

Ecology and behavior

''M. solifugus'' have a very narrow acceptable temperature range. Their metabolisms have adapted to cold temperatures., and they are the only known worm to spend their entire life in temperatures near 0 C (32 °F), where they are most active and their ability to produce adenosine triphosphate (ATP) is at its peak. They freeze at around −6.8 °C (19.8 °F), and their bodies decompose after continuous exposure to temperatures above 5 °C (41 °F). This decomposition process, known as autolysis, occurs when the cells produce digestive

enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products. A ...

s and self-destruct. The body, figuratively, melts. Even if other places are equally cold, ice worms never venture onto any other terrain. They eat the abundant

snow algae Snow algae are a group of freshwater micro-algae which grow in the alpine and polar regions of the earth. These algae have been observed to come in a variety of colors associated with both the individual species, stage of life or topography/geogra ...

and

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...

carried by the wind. Ice worms are most active in late spring. In the summer, they follow a diurnal cycle—at the first light in the morning, they sink into the glacier. A few hours before sunset, they poke out from the snow. In this respect they resemble some other oligochaetes that avoid strong radiation but are attracted to dim light. Little is known about the ice worm during the winter as the inaccessibility of glaciers prevents further study. Since in the winter the surface temperature on a glacier can reach −40 °C (−40 °F), the worms most likely remain below the surface. They may burrow as deep as several feet into the glacier in search of an area with a favorable temperature. The snowfall provides insulation, and the temperatures below remains a stable 0 C (32 °F). Ice worms can still find plenty of algae in the firn layer, the layer of packed snow in transition to ice. In glacial ponds or small streams, ice worms can be found in broad daylight. The freezing water provides the worms with a comfortable temperature, countering any heating of their dark bodies from the sun. In fast-flowing glacial streams, ice worms cling to the ice surface. Researchers have observed the worms gyrating their heads in the stream, possibly catching algae and pollen carried by the water. In still ponds, ice worms gather in bundles. Researchers speculate this is reproductive behavior. Ice worms do not graze in groups on the surface, so the contact in still ponds provides the rare opportunity for breeding. Ice worms move on the surface of ice at about 3 m/h (meters per hour) and move through snow by squeezing between the grains. Lateral movement is usually along the surface of the glacier and they penetrate the glacier vertically.

Research studies and medical uses

Researchers are investigating what prevents the worm from freezing at temperatures below 0 °C (32 °F) and are looking at the evolutionary steps by which the ice worm diverged from related species. Understanding the ice worm's physiology could suggest means by which to preserve organs for transplantation and could aid in the understanding of potential

extraterrestrial life Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might ...

on cold planets, as well as species on Earth which survive in climates colder than previously thought possible.

References

Sources

* Hartzell, P. (2003). Glacial Ecology: North Cascades Glacier Macroinvertebrates. Retrieved on Oct. 21, 2005, from: https://web.archive.org/web/20051212000121/http://nichols.edu/departments/Glacier/bio/index.htm * Pelto, M. S. (2003). Ice Worms (Mesenchytraeus solifugus) and Their Habitats on North Cascade Glaciers. A study by North Cascade Glacier Climate Project. Retrieved on Sept. 28, 2005, from https://web.archive.org/web/20090209012557/http://www.nichols.edu/departments/glacier/iceworm.htm * Shain, D. H., Carter M. R., Murray, K. P., Maleski, K. A., Smith, N. R., McBride, T. R., et al. (2000). Morphologic Characterization of the Ice Worm Mesenchytraeus solifugus. Journal of Morphology, 246, 192-197. * Shain, D. H., Mason, T. A., Farrell, A. H., & Michalewicz, L. A. (2001). Distribution and behavior of ice worms (Mesenchytraeus solifugus) in south-central Alaska. Canadian Journal of Zoology, 79, 10, 1813-1821.

External links

Dr. Daniel H. Shain @ Rutgers University
{{Taxonbar, from=Q143694 Enchytraeidae Animals described in 1898 Taxa named by Carlo Emery Fauna of the Northwestern United States Fauna of Western Canada