Ultrastructural analysis of the morphology and function of the spermatheca of the pulmonate slug Arion subfuscus

Abstract

A study of the histology, histochemistry and ultrastructure of the spermatheca of Arion subfuscus in different stages of its life cycle shows that the spermatheca, an accessory organ of the femal genital tract of pulmonates, is a spherical-shaped organ lined with a columnar and non-ciliated epithelium surrounded by a thin network of connective tissue with some muscle fibres. The narrow epithelial cells possess numerous microvilli that, excepting young specimens, are provided with long, thin and generally curved, membranous process. Golgi apparatus, RER and mitochondria are abundant. Basal infolds are not very deep. In specimens killed two days after-copula, the spermatheca is swollen and its lumen is full of degenerating spermatozoa, mucus masses and spermatophore fragments. The apex of the cell is rich in granules with varied content, including multivesicular bodies. In specimens killed two weeks after-copula there are numerous endocytic vesicles in the apex and big vacuoles containing lipid. It is considered that after mating the excess of exogenous spermatozoa and copulatory seminal fluids are digested in the spermatheca. First, there is extracellular digestion that may be carried out by the enzymes contained in the multivesicular bodies exocytosed to the lumen, as well as by the enzymes secreted in apocrine vesicles. The partially digested materials would then be absorbed by endocytosis and further digested intracellularly. The great accumulation of lipid in the epithelial cells two weeks after mating suggest that the spermatheca could be involved in lipid synthesis, acting as a reserve organ.