Return to C. Geographus
"C. magus is characterized by a remarkable conchological divergence between separate populations....Within the same population, C. magus may be either largely uniform or fairly variable in shell morphology."
Manual of Living Conidae (1995)
The species does indeed display exceptional variability in the pattern and coloring of its shell, with specimens looking as different as the locations where they were found.
Like all piscivorous cone shells, C. magus ("The Magician's Cone") must quickly immobilize its prey if it is not to be injured by the violent thrashing of a captured fish. Hunting at night or buried in the sand, the scent of nearby prey is detected in the water constantly inhaled through its siphon and passed over the gills. The snail's proboscis then is extended, its long narrow tip holding a hollow radular tooth which, when it comes into contact with a fish, harpoons it. Simultaneously, a complex medley of conotoxins is injected, eliciting almost immediate excitotoxic shock. The proboscis is retracted and the paralyzed fish, its nerve cells damaged or killed by the over excitation of neurotransmitters, pulled into the distended mouth.
The phenomenon is little different for the novice collector who holds a C. geographus too long in the palm of the hand or, more imprudently, begins to scrap away the shell's protective periostracum to see what is beneath. The agitated snail within extends its proboscis (sometimes as long as the shell itself) and inject the same complex of conotoxins, all of which have evolved to disrupt the various channels that control the transmission of electrical impulses within cells, and thereby block the passage of ions across the cell membrane. Alpha-conotoxins, for example, inhibit acetylcholine, the neurotransmitter that conducts nerve and muscle impulses. Others disrupt sodium, calcium, and potassium channels. Receptors are bound or inhibited, voltage-gated ion channels closed or kept open, electrical impulses surge or do not fire. The neuromuscular system shuts down, and there is convulsion, arrhythmia, and paralysis.
Aside from its variability, Conus magus also is known for a peptide in its cone venom that was discovered by an undergraduate student working in the laboratory of Baldomero Olivera. Synthesized and marketed as Prialt (Ziconotide), it is considered a primary alternative (hence the name) to morphine in the management of intractable neuropathic pain. Unlike an opiate receptor, which becomes less efficacious over time, the synthesized form of the conotoxin acts directly on the calcium channel by blocking the synapse from the pain fiber to nerve cells in the spinal cord, thereby inhibiting the release of neurotransmitters to the brain. Although efficacious, the drug must be administered intrathecally, directly into the spine.
Prialt, in fact, is the synthetic analog of only one of approximately one-hundred components in the venom of C. magus. Given that cone snails, which number between 500 and 700 species, produce their own unique set of conotoxins, each numbering between 50 and 200 peptides, tens of thousands of possible combinations have evolved, each specific to the animal being hunted, whether a marine worm, other mollusks, or small fish.
The picture of Conus Magus shows some of the variety in the patterning of its shell.
References: Linnaeus: Systema Naturae (1758), 10th ed. (p. 716, no. 276); "Ziconotide for Treatment of Severe Chronic Pain" (2010) by A. Schmidtko, J. Lötsch, R. Freynhagen, and G. Geisslinger, Lancet, 375(9725), 1596-1577; Manual of the Living Conidae (1995) by Dieter Röckel, Werner Korn, and Alan J. Kohn; "Conus Venoms: A Rich Source of Novel Ion Channel-Targeted Peptides" (2004) by Heinrich Terlau and Baldomero M. Olivera, Physiological Reviews, 84(1), 41-68; "Pharmacological Study of the Venom of the Gastropod Conus Magus" (1965) by R. Endean and Joan Izatt, Toxicon, 3(2), 81-93; "Pharmacology of the Venom of the Gastropod Conus Magus" (1974) by R. Endean, P. Gyr, and Glenda Parish, Toxicon, 12(2), 117-129; "The Venom Apparatus of Conus Magus" (1967) by R. Endean and Claudine Duchemin, Toxicon, 4(4), 275-284.
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