Tardigrada

Tardigrada

Languages: English

Overview

Brief Summary

The Tardigrada are microscopic animals that look superficially like miniature eight-legged teddy bears. They live in habitats with at least intermittent moisture and can form resistant resting stages enabling them to endure extreme environmental conditions, including intense heat and cold, radiation, desiccation, even the vacuum of space. As of 2002, about 900 species had been described, but it’s likely that many more are still to be discovered.

(Becquerel, 1950; Crowe et al., 1998; Nelson, 2002; Ruppert et al., 2004; Horikawa et al., 2006; Jönsson et al., 2008)

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Description

Behaviour

When environmental conditions become unfavorable, tardigrades can enter a state of dormancy called “cryptobiosis,” which is characterized by desiccation, reduced metabolic rate, and enhanced resistance to conditions such as drought, low oxygen, salinity changes, or extreme temperatures. A dormant tardigrade, called a “tun,” may survive for long periods – 10 to 100 years, alternating between periods of activity and dormancy. (Nelson, 2002; Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Morphology

Tardigrades are bilaterally symmetrical, usually “plump” and roughly cylindrical. Superficial form appears to be organized into five segments: a short head and a trunk of four segments, though the trunk may actually have 4 to 5 segments and the head 3 segments. Stubby legs are borne on each trunk segment, each having 4 to 8 retractile claws at the ends. The epidermis secretes a complex cuticle, which in some species is elaborated with structures like spines, granules, and pores. The cuticle is molted periodically. Tardigrades can be translucent or opaque, and the cuticle or gut may be colored brown, green, orange, pink, red, or yellow (Nelson, 2002; Ruppert et al., 2004)

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Physiology

Because tardigrades are so small, they have a high surface-area to volume ratio, making specialized gas exchange structures unnecessary. Diffusion across the body surface is sufficient. The nervous system is similar to that of arthropods, onychophorans, and annelids, with a lobed dorsal brain and ventral nerve cord with fused ganglia. (Nelson, 2002; Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Size

Body length is typically 100 to 150 micrometers, but there are that reach lengths of 1.5 mm (Nelson, 2002; Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Ecology

Habitat

Tardigrades are found in a variety of wet or moist habitats, including marine and freshwater, moist soils, hot-springs, glaciers, mosses, lichens, leaf-litter. In environments with intermittent moisture, tardigrades can enter a “cryptobiotic phase” that allows them to survive dry periods. (Nelson 2002; Ruppert et al., 2004)

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Distribution

Worldwide.

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Trophic Strategy

Trophic strategies vary.  Most tardigrades feed on the cytoplasm of plant cells. Those living in soil eat algae, probably detritus, and some are predators, feeding on other microscopic soil animals, including nematodes and other tardigrades (Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Dispersal

The dormant state of cryptobiosis facilitates dispersal – the dried “tuns” are easily transported by winds or other animals (Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Life Expectancy

10 to 100 years (Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Reproduction

Most tardigrades are either female or male (“gonochoric”), though a few species are hermaphroditic. And males are absent in some parthenogenetic genera. (Nelson, 2002; Ruppert et al., 2004).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Evolution and Systematics

Systematics and Taxonomy

“Recent molecular analyses and additional morphological studies of the nervous system have confirmed the phylogenetic position of tardigrades as a sister group of the arthropods.” (Nelson, 2002)

However according to Ruppert et al. (2004), evolutionary relationships are currently uncertain.  Though they seem to be closest to arthropods, there is also similarity to cycloneuralians (Kinorhynchans, Loriciferans, Priapulids, Nematodes, and Nematomorphs).

Author(s): Soulanille, Elaine
Rights holder(s): Soulanille, Elaine

Taxonomic Children

Total: 2

Hypsibius dujardini (Doyère, 1840), New taxon

References

Becquerel, P. (1950).  La suspension de la vie au dessus de 1/20 K absolu par demagnetization adiabatique de l’alun de fer dans le vide les plus eléve. Comptes Rendus de l'Académie des sciences. 231, 261-263.
Convey, P., & McInnes S. J. (2005).  Exceptional tardigrade-dominated ecosystems in Ellsworth Land, Antarctica. Ecology. 86(2), 519 - 527. Abstract
Crowe, J. H., Carpenter J. F., & Crowe L. M. (1998).  The role of vitrification in anhydrobiosis. Annual Review of Physiology. 60(1), 73 - 103. Abstract
Gabriel, W. N., McNuff R., Patel S. K., Gregory T. R., Jeck W. R., Jones C. D., et al. (2007).  The tardigrade Hypsibius dujardini, a new model for studying the evolution of development. Developmental Biology. 312, 545-559.
Gordon, D. P., Beaumont J., MacDiarmid A., Robertson D. A., & Ahyong S. T. (2010).  Marine Biodiversity of Aotearoa New Zealand. PLoS ONE. 5(8), e10905.
GUTZMANN, E., Arbizu P. M., ROSE A., & Veit-Kohler G. (2004).  Meiofauna communities along an abyssal depth gradient in the Drake Passage. Deep Sea Research Part II: Topical Studies in Oceanography. 51(14-16), 1617 - 1628.
Hinton, H. E., & Needham A. E. (1968).  Reversible Suspension of Metabolism and the Origin of Life [and Contribution to the Discussion]. Proceedings of the Royal Society of London. Series B, Biological Sciences. 171, 43-57.
 
Horikawa, D. D., Sakashita T., Katagiri C., Watanabe M., Kikawada T., Nakahara Y., et al. (2006).  Radiation tolerance in the tardigrade Milnesium tardigradum.. International journal of radiation biology. 82(12), 843-8. Abstract
Jönsson, I. K., Rabbow E., Schill R. O., Harms-Ringdahl M., & Rettberg P. (2008).  Tardigrades survive exposure to space in low Earth orbit.. Current biology : CB. 18(17), R729-R731. Abstract
Jönsson, K. I., E R., Schill R. O., Harms-Ringdahl M., & Rettberg P. (2008).  Tardigrades survive exposure to space in low Earth orbit. Current Biology. 18, R729-R731.
Kristensen, R. M. (2009).  The first record of cyclomorphosis in Tardigrada based on a new genus and species from Arctic meiobenthos1. Journal of Zoological Systematics and Evolutionary Research. 20(4), 249 - 270. Abstract
Matthews, G. B. (1938).  Tardigrada from North America. American Midland Naturalist. 19, 619-627. Abstract
Maucci, W. (1996).  Tardigrada of the Arctic tundra with descriptions of two new species. Zoological Journal of the Linnean Society. 116(1-2), 185 - 204. Abstract
McInnes, S. J., & Pugh P. J. A. (1998).  Biogeography of limno-terrestrial Tardigrada, with particular reference to the Antarctic fauna. Journal of Biogeography. 25(1), 31 - 36. Abstract
Miloslavich, P., Díaz J M., Klein E., Alvarado J J., Díaz C., Gobin J., et al. (2010).  Marine Biodiversity in the Caribbean: Regional Estimates and Distribution Patterns. PLoS ONE. 5(8), e11916.
Moon, S Y., & Kim W. (1996).  Phylogenetic position of the Tardigrada based on the 18S ribosomal RNA gene sequences. Zoological Journal of the Linnean Society. 116(1-2), 61 - 69. Abstract
Nelson, D. R. (2002).  Current Status of the Tardigrada: Evolution and Ecology. Integrative and Comparative Biology. 42(3), 652 - 659. Abstract
Nelson, D. R., & Marley N. J. (2000).  The biology and ecology of lotic Tardigrada. Freshwater Biology. 44(1), 93 - 108. Abstract
Nichols, B. P., Nelson D. R., & Garey J. R. (2006).  A Family Level Analysis of Tardigrade Phylogeny. Hydrobiologia. 558(1), 53 - 60. Abstract
Ruppert, E. E., Fox R. S., & Barnes R. D. (2004).  Invertebrate Zoology: a Functional Evolutionary Approach. 963 plus index. Belmont, CA: Thomson Learning, Inc. - Brooks/Cole.
Somme, L., & Meier T. (1995).  Cold tolerance in Tardigrada from Dronning Maud Land, Antarctica. Polar Biology. 15(3),  Abstract
Telford, M. J., Bourlat S. J., Economou A., Papillon D., & Rota-Stabelli O. (2008).  The evolution of the Ecdysozoa. Philosophical Transactions of the Royal Society B: Biological Sciences. 363(1496), 1529 - 1537. Abstract
Wright, J. C. (1991).  The significance of four xeric parameters in the ecology of terrestrial Tardigrada. Journal of Zoology. 224(1), 59 - 77. Abstract
Wright, J. C., Westh P., & Ramløv H. (2010).  Cryptobiosis in Tardigrada. Biological Reviews. 67(1), 1 - 29.
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