Aurelia aurita is a cosmopolitan species that is common along the coasts of the Gulf of Mexico. It enters lagoon–estuarine systems where it is present in high densities. The karyotype of organisms from Estero Tenechaco, Tuxpan, Veracruz is described. Specimens were collected with a spoon landing net in March 2003. Marginal tentacle tissue was subjected to cytogenetic processing, including a mitostatic treatment previous to hypotonic shock. The chromosome numbers obtained were 2n=44 and n=22, and the fundamental number was NF:88.