Isozymic differentiation of two sibling species of Squatina (chondrichthyes) in South Brazil.

Two sympatric morphotypes of the nominal species Squatina argentina from South Brazil are compared by the frequencies of 25 isozymes distributed over 14 presumptive loci. The Nei's Genetic Identity index obtained in a comparison of the populations is of 0.71. The loci EST-2 and EST-4 are fixed at different isozymes for each population, indicating a reproductive isolation between them. The most significant morphological and meristical differences between the morphotypes are the presence or absence of dorsal spines and the dental formula. The agreement between these characteristics and the genetical data indicates that the two morphotypes belong to different species.