Cone shells are carnivorous marine snails, distributed throughout tropical and subtropical seas. Known as toxoglossans (or poison tongues), these gastropod mollusks have developed an awesome apparatus for stinging and capturing their prey. Feeding primarily on small fish, worms and other marine snails, cones capture and paralyze their victims with an arrow-like harpoon filled with potent venom. Like the blowgun hunters of the Amazon, a cone stalks its unsuspecting quarry with a long elastic tube armed with the deadly dart. At close range the needle sharp arrow is ejected, penetrating the soft body of the victim. Within seconds the paralytic venom immobilizes the prey, which is engulfed whole into the cone’s distended mouth.
The lethal barbed spear is actually a modified tooth known as a radula. In nearly all gastropods the radula apparatus consists of a horny ribbon bearing rows of hooked teeth used for scraping food material from hard surfaces. But in cones the radular teeth have evolved into hypodermic-like needles, barbed at the tip. The shape and size of radular teeth vary considerably among cone groups. Some are long, slender and strongly barbed at the tip, whereas others can be short with weak barbs. The stinging arsenal consists of several radulae held in reserve in the radula sac. As many as 75 may be present in some species. When one is discharged another is transported to the tip of the elastic tube (proboscis) ready for firing.
The venom is a protein base neurotoxin produced in a thin, serpentine duct, reaching more than two feet in length in larger species. A kidney-shaped bulb connected to the duct functions as a pump by forcing the venom through the duct into the hollow radula.
In recent years, marine toxicologists have investigated the nature of the venom from several dangerous species. It was discovered that the toxic components in the venom are proteins, known as peptides, which produce paralytic effects on test animals. Venom studies of Conus geographus indicate that the toxin affects the junction between the muscle and nerve causing muscle paralysis. Test mice injected with this venom experienced convulsions and paralysis of limbs, followed by death from respiratory failure minutes after envenomation.
Based on food preference, cones can generally be divided into three groups: (1) Molluscivorous cones, such as Conus dalli, which feed exclusively on mollusks, including other cones; (2) Vermivorous species whose diet is restricted to worms; and (3) Piscivorous cones, such as Conus geographus, which prey exclusively on small fish. The potency of the venom varies between each group and among species. All of the 350-400 species are venomous but their toxins are directed at affecting specific preys. The venom of a fish eating species, for example, is usually not effective against worms or mollusks; molluscivorous cones cannot paralyze fish or worms. Cones such as Conus brunneus, a vermivorous species, are highly specialized in their food preference; they do not select any species of worm indiscriminately. Equipped with an ultrasensitive chemical sensor for locating prey, they seek out only the bristle-bearing fire worms. In contrast, molluscivorous cones are less specialized. Conus dalli, for example, will prey on a variety of mollusks, even other cones.
Piscivorous species, particularly Conus geographus, are responsible for most serious human injuries and fatalities. But one molluscivorous cone, Conus textile, has been implicated with at least one fatality. Although the venom of vermivorous cones is not considered lethal to man, some species could be potentially dangerous because of their large size. One of the largest vermivores, Conus betulinus, can reach seven inches in length and can produce a comparatively large quantity of venom.
Victims of cone stings experience a variety of systemic effects. Mild cases may result only in a burning rash or blurred vision, lasting less than an hour. Serious stings, however, can involve nausea, convulsions, tissue necrosis and flaccid paralysis of the limbs lasting for weeks. Respiratory and cardiac arrest follow in fata cases. A common complaint by recovering patients is the constant presence of extreme weakness. Since there is no efficient antivenin against cone venom, treatment is largely symptomatic, directed at relieving pain and halting the deleterious effects of the poison.
Stings are usually the result of careless handling by shell collectors. Although most species retract within the shell when handled, some remain active shortly after collection and may become aggressive. Conus textile, responsible for at least one confirmed human fatality, is particularly active and aggressive after collection. Such animals should not be handled without gloves.