ABSTRACT. Description of the reproductive cycle of Donax hanleyanus (Bivalvia, Donacidae) in southern Brazil. The changes in gonadal development in male and female of Donax hanleyanus Philippi, 1847 are described. Gonad development and spawning seasons were assessed by monthly sampling of population from Arroio Teixeira beach, southern Brazil. Histological examination of clams showed in the most of the adult population sampled that the spawning is practically continuous, without any period of sexual rest. There are two main periods of gametogenesis, in winter and in summer, being the degree of maturation longer in the latter. The water temperature is stimulant on gametes proliferation and spawning.

ABSTRACT. Biological cycle of Simpulopsis ovata (Gastropoda, Bulimulidae) in São Francisco de Paula, Rio Grande do Sul, Brazil. The population growth of Simpulopsis ovata (Sowerby, 1822) from the Centro de Pesquisas e Conservação da Natureza -Pró-Mata, São Francisco de Paula, Rio Grande do Sul, Brazil, was studied along eleven months of 1996. Two discontinuous age classes were identified. The first one, with a monthly growth rate of 1.55 mm, was reproductively mature during April and May. The second one appeared after the previous group and had a monthly growth rate of 0.44 mm. The fact that no adults from the two age classes were found together is a characteristic of a semelparous species. New insights about its shell, pallial cavity and reproductive system are given. This is the first record of S. ovata for the State of Rio Grande do Sul.

Foi avaliada a proporção sexual e determinado o tamanho da concha, quando da primeira maturação sexual de uma população de Donax hanleyanus Philippi, 1847, amostrada durante 15 meses, entre outubro de 2001 e dezembro de 2002, na praia de Arroio Teixeira, sul do Brasil. Aproximadamente, 3000 espécimes foram coletados na zona de varrido, com comprimento de concha igual ou superior a 2,0 mm. A análise histológica foi realizada em 347 espécimes, entre 7,0 e 28,33 mm de comprimento de concha. A proporção sexual é de 1:1. Os diferentes métodos utilizados, para determinação do tamanho da primeira maturação sexual, resultaram em comprimentos aproximados, podendo-se concluir que Donax hanleyanus atinge a maturidade em um comprimento médio de concha entre 12,28 e 12,60 mm. Sugere-se que o comprimento mínimo de captura seja estabelecido em 15,0 mm.