CAPRIOLI*, Manuela*; RICCI, Claudia; SANTO, Nadia; Univ. di Milano, Milano; Univ. di Milano, Milano; Univ. di Milano, Milano: Changes in a bdelloid rotifer entering desiccation

Fine morphology (Scanning Electron Microscope, Confocal Laser Scanning Microscope) and metabolism (calorimeter) of a bdelloid rotifer, Macrotrachela quadricornifera, were studied to illustrate the morphological and metabolic changes that seem to be responsible for successful recovery after anhydrobiosis. In response to desiccation, bdelloids withdraw head and foot, sealing them into the trunk, and attain the �tun� shape. At the end of this process the rotifer reduces its body volume and loses about 75% of its weight. It is likely that the weight loss is mainly due to water loss, possibly from the main body cavity (pseudocoel). Attainment of the tun shape implies contraction of the longitudinal muscles, which appear tied in the hydrated rotifer but loose in the dormant rotifer. We hypothesize that the body cavity of the dormant bdelloid loses its internal fluids, and that this hampers its role as hydroskeleton and prevents movements. In other words, the tun shape of the anhydrobiotic rotifer is not maintained by musculature contraction, but by the reversible absence of hydroskeleton. Metabolism of a hydrated active bdelloid is about 0.01 &microW by an isotherm calorimeter; no metabolic activity is detectable in the anhydrobiotic rotifer. Unlike most anhydrobiotic animals, bdelloids lack trehalose as a protective chemical: no trehalose was found in M. quadricornifera. What molecules are involved in the protection of the bdelloids� biological structures from the injuries due to desiccation is still an open question.