Two species of large jelly-fish Aurelia aurita L. and Stomoiophus meleagris Ag, have been registered within a yearly cycle at the system of coastal lagoons "Carmen-Machoria-Redonda ", South of the Gulf of Mexico. A. aurita showed two well defined periods: autumn/winter with predominant young specimens (25 to 100 mm) and spring/summer with a wide adult distribution (200 to 400 mm), beeing the juveniles restricted to the internal, regions of the system. S. meleagris gave evidence of adult populations all year round, the greatest population density occurred during the summer/autumn period with maximum sizes of 200 to 300 mm and during the winter/spring period, juveniles from 10 to 30 mm in December and 50 to 100 mm in April, giving a distribution pattern very similar to A. aurita.