Structural study of the ovary, oogenesis and brooding in Tonicia lebruni (Polyplacophora Chitonidae) from Patagonia

Abstract

Tonicia lebruni, a common, lower intertidal and subtidal chiton inhabiting Patagonianrocky shores, is a gonochoristic iteroparous species producing large eggs( 400 lm in diameter), which are fertilized and brooded within the pallialgroves until released as juveniles. A free larval stage is absent, despite this, T. lebruniis widely distributed along the south-western Atlantic. At Puerto Deseado,T. lebruni has a marked seasonality in the reproductive cycle, reproducing onlyonce a year. The reproductive period is quite short and defined in time: spawningand brooding take place during the late austral winter and beginning ofspring. Recovery of the female gonad starts very soon after spawning. Oogenesistakes about 10?11 months for completion. Brood size is correlated with lengthof maternal individual. The number of embryos per brood varied between 785and 5945. Extensive resorption of abortive eggs is viewed as related to limitationof space available for brooding. The egg hull is formed by a large number of minutepentagonal or hexagonal plates each one bearing a short spine bent onto theegg surface. The morphology and the surface of the hull could contribute to thecohesiveness of the brooded egg mass within the pallial grooves.