Comparative structure of the lateral pedal defensive glands of three species of Siphonaria (Gastropoda: Basommatophora)

Abstract

Histology and electron microscopy were used to describe and compare the structure of the dorso-lateral pedal defensive glands of three species of marine Basommatophora, Siphonaria capensis, S. serrata and S. gigas. All three species possessed multicellular glands, but these were largest and most abundant in S. capensis. In S. capensis and S. serrata, defensive glands were composed of two types (type I and II) of large secretory cells filled with product and some irregularly shaped support cells that surrounded a central lumen. The product of both cell types was produced by organelles confined to the bases of the cells. The entire gland was surrounded by a well-developed layer of smooth muscle and collagen. Type I cells stained positively for neutral and sulphated mucins, and observed with transmission electron microscope (TEM) the product had a reticulate appearance. By contrast type II gland cells stained positively for acidic mucins and the secretory product was formed as large granular vesicles. The products from both types of cell, which appeared to be secreted by holocrine secretion, mixed in the lumen of the duct. Individuals of S. gigas had two types of lateral pedal glands, a large multicellular type and a tubular unicellular gland. The multicellular glands, which were surrounded by poorly developed muscle, contained one type of gland cell that stained for neutral and sulphated mucins only, as well as some support cells. The tubular glands contained a heterogeneous product that stained positively for neutral and sulphated mucins.