Nutrition & Uptake

The marbled cone snail partially buried under the substrate (Courtesy of Jeanette and Scott Johnson)As described on the Adaptation page, Conus marmoreus and all the other cone snails have adapted an altered radular tooth.  To catch its prey off guard, the marbled cone buries itself into the sandy substrate with only its siphon sticking out to detect prey.  When prey is near and this modified radular tooth is in position to be shot, the muscular poison bulb at the end of the venom bulb contracts.  The resulting pressure shoots the harpoon out of the proboscis and into its prey, followed by a cloud of poison.  Molluscivores (mollusk eaters) such as C. marmoreus may use several harpoons in succession, and the poison is exuded through a canal in the tooth.  Watch the video below to see exactly how it takes down its prey (pay close attention to 0:49 to see the cloud of poison; video courtesy of Dr. Jason Biggs).
Because mollusk prey can’t escape as quickly as fish, there is no need for the molluscivores to hold on to their prey after they have harpooned them, as piscivores (fish eaters) do.  If its prey has a thin shell, the marbled cone snail will ingest the whole shell; however, if the Conus marmoreus sucks a snail out of its shell (Courtesy of Jeanette and Scott Johnson)shell is too thick, it will hold its mouth against the prey’s opening and will suck out the snail inside (shown left).  When its prey is ingested, the tooth is swallowed whole as well, and a new one is moved into the base of the proboscis for a future attack.  The poison used by C. marmoreus is ingested along with the prey, but has no effect on the snail itself.  More information on this poison can be found here.  There are no distinct shell differences between deadly fish-feeding species and less-extreme worm eating species of carnivorous snails, so one should be very careful when collecting or examining shells.

Conus marmoreus in the middle of a meal (Courtesy of Jeanette and Scott Johnson)In order to get nutrients cycled throughout its body, C. marmoreus utilizes what is called an open circulatory system.  In this system, organs are bathed with transport fluid, instead of being confined to blood vessels like in closed circulatory systems.  The transport fluid is hemolymph, which is made up of blood and interstitial fluid.  It also contains hemocytes, which function as a form of defense to antigens, and uses hemocyanin as an oxygen carrier instead of hemoglobin. An open circulatory system favors organisms with a sedentary lifestyle and low oxygen demands since it has low vessel pressures, which perfectly describes the marbled cone snail.

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