BEHAVIORAL-MODIFICATIONS OF LIRIOPE TETRAPHYLLA (CHAMISSO AND EYSENHARDT) (CNIDARIA, HYDROZOA, TRACHYMEDUSAE) INDUCED BY HYPOSMOTIC CONDITIONS

The osmoregulatory capability and swimming behavior of Liriope tetraph ylla (Chamisso and Eysenhardt) were analyzed under hyposmotic conditio ns. These hydromedusae are shown to be osmoconforming animals that are not able to maintain constant osmotic and ionic concentrations of the ir body fluids when exposed to anisosmotic media. Swimming behavior (a s measured by the pulsation rate and the swimming index) is transientl y affected by osmotic shock, being restored 30 min after exposure. How ever, even when swimming activity was restored, two different swimming patterns were observed depending on the hypotonic period. Thirty minu tes exposure led to an increase of the quiescent period with no change s on the swimming burst characteristics while five hours exposure to h ypotonicity shortened both the quiescent period and burst durations. S uch behavioral modifications were related to the changes in body fluid ionic composition (mainly to extracellular K+ levels) that occur duri ng the osmotic adjustment process. The fact that swimming activity was impaired during hypoionic shocks and this condition caused morphologi cal changes in the animals suggests that these early metazoans are end owed with mechanisms to compensate for ionic gradient changes induced by hyposmotic, but not for the ones caused by hypoionic condition.