Hypobranchial gland
The hypobranchial gland is a glandular structure which is part of the anatomy of many mollusks, including several different families of gastropods, and also many protobranch bivalves. This gland produces mucus as well as biologically active compounds. The cephalopod ink sac is a modified hypobranchial gland. The hypobranchial gland is found in many sea snails, including those in the families Haliotidae, Buccinidae, Mitridae and Costellariidae. It usually presents itself as a thickening of the tissue located in the roof of the animal's mantle cavity. Its morphology, however, is variable between different groups of snails. In the aculifera  the hypobranchial glands are referred to as "mucus tracts" and occupy a posterior position in the body. Human use. There have been studies on some species within the family Muricidae, because in those species this gland secretes the precursor to the historically important natural dye, Tyrian purple.