THE VENOM APPARATUS OF THE GLOBIFEROUS PEDICELLARIAE OF THE TOXOPNEUSTID SPHAERECHINUS-GRANULARIS (ECHINODERMATA, ECHINOIDA) - FINE-STRUCTURE AND MECHANISM OF VENOM DISCHARGE

Globiferous pedicellariae of Sphaerechinus granularis are venomous def ensive appendages consisting of a stalk bearing a head made of three m ovable jaws. Each jaw is supported by a calcareous valve ending with a terminal grooved tooth. A venom apparatus is located in each jaw and consists of a venom gland surrounded by a muscular envelope and termin ating in a duct which completely encircles the terminal tooth of the v alve. Contrary to previous statements, the duct does not lie inside th e groove of the terminal tooth. In mature pedicellariae, the venom is stored in intracellular vacuoles of highly differentiated cells which are no longer active. The cells rill the whole space of the venom glan d which is without a lumen; they are segregated into two types that oc cur in distinct regions and differ from each other by morphological an d staining properties of their secretions. Upon contraction of the mus cular envelope, the venom is released via a holocrine mechanism and in filtrates the predator's tissues through the wound inflicted by the th ree calcareous teeth of the valves. In no case is the venom emitted th rough the tooth groove.