The structure of the egg ribbons of a planktonic and intracapsular developing siphonariid limpet (Gastropoda: Pulmonata)

Abstract

Summary Egg ribbons of two sympatric species of siphonariid limpets (Siphonaria capensis and Siphonaria serrata) with different life-history strategies were studied to compare their structural and biochemical differences. The structure of the egg ribbons was examined by light, transmission and scanning electron microscopy. The organic content of the egg ribbons was determined by TCA soluble carbohydrate, NaOH soluble protein and total lipid estimation. In both species histochemical tests showed the presence of mucopolysaccharides in the egg ribbon jelly, perivitelline fluid and the developing embryo, and protein in the perivitelline fluid and the developing embryo, whereas lipid was present only in the developing embryo. The egg ribbons of both species consist of (proceeding inwards) an outer mucous cover, a mucous matrix which holds the egg capsules, an inner mucous layer terminating in a mucous strand, egg capsules and the envelope surrounding the perivitelline fluid. The structural composition of the egg mass was similar in both species although the spawn of S. serrata appeared more fibrous and had a greater amount of carbohydrate and protein than that of S. capensis. S. serrata, which has intracapsular development, also produces egg capsules with thicker walls compared to S. capensis. It is suggested that it is these differences that make the egg masses of S. serrata more robust, enabling them to survive on the shore for longer periods.