The hypobranchial gland from the purple snail Plicopurpura pansa (Gould, 1853) (Prosobranchia: Muricidae)

Results are presented on the histology of the hypobranchial gland of the marine muricid Plicopurpura pansa (Gould 1853). The general structure and secretory features were investigated using light microscopy and histochemical methods for the determination of tryptophan/indol. The hypobranchial gland off. pansa is an antero-posteriorly elongated organ located on the internal surface area of the mantle, that folds on its posterior side near the rectum, right of the ctenidia and anterior to the kidney. In dead animals it is easily distinguishable by-the purple color that develops after removing the shell. Parallel to the hypobranchial gland, in the same position, can be found a black-pigmented structure, presumably the anal gland. The secretory epithelium, which forms the hypobranchial gland consists of at least six different and very long (156.7 μm) cell types. It was impossible to distinguish clearly the different histological regions of the hypobranchial gland, because the different cell types were uniformly distributed throughout the gland, with the exception of the rectal area. The number of acidophilic granular cells differed markedly between animals, probably because of different levels of secretion. In the mantle cavity was always found a large quantity of mucus and only occasionally acidophilic granulated secretory products. Only the two cell types with acidophilic granules in the hypobranchial gland showed histochemically strong positive reactions for tryptophan, indicating in these cells high concentrations of the precursors for "Tyrian Purple".