Mollusca

The phylum Mollusca is the second largest in the animal kingdom. Most of the mollusca species are marine; they are represented in fresh water only by snails and mussels, and on land by snails and slugs. Their basic pattern of construction has four divisions: the head with the mouth, the dorsal ventral sack, the ventral foot, and the mantle. The respiratory organs are contained in the mantle cavity situated between the mantle and the visceral sack. There is no internal skeleton. The snails (Gastropoda) represent the largest section of the Mollusca. The mantle, in this class, generally secretes a spiral or bowl-shaped shell made up of two or three layers: the outer uncalcified periostracum, the middle layer made up of the ostracum consisting of several layers of calcite or arragonite, and in some spiecies this is followed by a layer of mother-of-pearl.

Shells belonging to the families Turridae and Conidae have a hollow tooth which is connected to a poison gland. Shells belonging to the Turridae have longish oval or spindle-shaped shels curved in along the whorl seams; those belonging to the Conidae are conical short spiral with high terminal whorls, a long narrow aperture and a correspondingly shaped operculum. These toxic stinging shells are found in the warm waters of the Indo-Pacific, Australia and New Zealand, Southern Calfornia, and the Mediterranean. The different species in these families can fire a barbed harpoonlike device from a slit in their shell to obtain food and to protect against predators. The cone shell uses its sting to secrete a neurotoxin that competes for acetylcholine in the body. Their food consists of worms, mollusks or fish. The fish feeding variety of cones are the most dangerous to humans. These can cause death within 15 minutes. The Mediterranean species Philbertia purpurae bicolor and Conus mediterraneus are not as dangerous as those found in the tropics.

Another member of the phylum Mollusca are the octoposes or cephalopoda. These have a parrot-like beak and can inflict a painful bite. These bites are rarely serious and should be managed as lacerations.

Clinical Features: With injection of the toxin, the injection site becomes initially very painful and subsequently the surrounding skin becomes insensitive and bluish. The poison may be systemically absorbed to cause a slight generalized weakness of the body, associated with generalized numbness, tingling or itching of the skin. With very toxic species, neurological symptoms would be more severe leading to ataxia, breathing problems, difficult swallowing, paralysis, coma and death.

Treatment: The treatment of Conus stings is largely empirical. As first aid, it is essential to clean the wound throughly with fresh or salt water, and to provide a strong pain-killer. The affected area should be soaked in hot water or covered with a hot compress. The water should be very hot (circa 122 F), so that the heat will deactivate the poison. This will generally suffice for the less toxic species. For more toxic species, continue applying hot water for 30 minutes to an hour. The patient should lie still with the stung part immobile and lower than the heart. Tie a venous tournique around a stung limb two or four inches above the sting. If the swelling reaches the band, tie another veroun tournique two or four inches higher up and remove the first one. Local injection of epinephrine and subsequent use of neostigmine has been suggested for the management of severe toxic species poisoning. Mechanical ventilation and measures to combat shock will be needed.