WEBVTT - How Do Snails Grow Their Shells? 0:00:02.040 --> 0:00:07.120 Welcome to brain stuff from how stuff works, Hey, brain stuff, 0:00:07.160 --> 0:00:12.119 Lauren Vogel bomb Here. Snails are very attached to their shells. Literally, 0:00:12.640 --> 0:00:15.800 these slow moving mollusks grow protective shells to which they 0:00:15.840 --> 0:00:20.079 are physically connected. Eviction means death. No snail can survive 0:00:20.160 --> 0:00:24.200 being torn away from its private calcified fortress. But how 0:00:24.239 --> 0:00:27.640 exactly do snails shells develop and what sets them apart 0:00:27.680 --> 0:00:30.600 from other types of animal armor? Before we get to 0:00:30.640 --> 0:00:33.720 that A bit of snail one oh one. The total 0:00:33.840 --> 0:00:36.400 number of snail species could be as high as forty 0:00:36.440 --> 0:00:39.480 three thousand. Most of us are familiar with land based 0:00:39.560 --> 0:00:42.519 varieties or those that live in ponds, but marine snails 0:00:42.560 --> 0:00:46.159 also exist, and when it comes to procreation, certain species 0:00:46.200 --> 0:00:50.640 reproduce sexually, while others are self fertilizing hermaphrodites. Whatever gets 0:00:50.680 --> 0:00:53.800 the job done right. They all do have one thing 0:00:53.840 --> 0:00:58.240 in common, though. Snails all hatch from eggs. Generally, the 0:00:58.360 --> 0:01:01.160 parents lay these eggs in loo soil or affix them 0:01:01.160 --> 0:01:04.560 to rocks, though a few species are over viviporous, meaning 0:01:04.600 --> 0:01:07.720 their eggs hatch inside the mother's body. The newborns then 0:01:07.800 --> 0:01:11.040 squirm out and face the world, but this brings us 0:01:11.040 --> 0:01:14.040 back to that question about the shell. It's during the 0:01:14.160 --> 0:01:17.479 gestation period that a snail's shell begins to form, and 0:01:17.560 --> 0:01:20.360 here's where the mantle comes in. This is a crucial 0:01:20.440 --> 0:01:23.840 organ possessed by mollusks such as snails. Its function is 0:01:23.920 --> 0:01:28.560 making and developing shells. Calcium carbonate is the primary ingredient 0:01:28.640 --> 0:01:31.360 in snail shells. Those small amounts of protein also go 0:01:31.440 --> 0:01:34.080 into the mix, so in order to build these shells, 0:01:34.319 --> 0:01:37.240 the mantle creates an electric current that helps the organism 0:01:37.280 --> 0:01:41.160 push calcium ions into the right places. Before hatching, a 0:01:41.240 --> 0:01:45.000 baby snail grows a protoconch, the first component of its shell. 0:01:45.560 --> 0:01:48.760 Once our little snail leaves the egg, healthy eating becomes 0:01:48.760 --> 0:01:52.800 a priority. The mantle will require additional calcium to strengthen 0:01:52.840 --> 0:01:56.840 and expand the shell. Instinct compels newborn snails to devour 0:01:56.920 --> 0:01:59.680 what's left of the calcium rich egg that they've just escaped, 0:02:00.120 --> 0:02:04.160 and thus begins a lifelong habit. Snails of all ages 0:02:04.160 --> 0:02:06.480 and sizes need to keep eating foods that are high 0:02:06.520 --> 0:02:09.200 in calcium. This is one reason why snails are so 0:02:09.280 --> 0:02:12.200 often considered pests. A few of them like to chow 0:02:12.280 --> 0:02:16.120 down on spinach, broccoli, turnip, and other calcium loaded crops. 0:02:16.639 --> 0:02:19.120 They can also get their calcium fixed by swallowing soil 0:02:19.280 --> 0:02:23.200 or gnawing on limestone. That protoconch comes with a small 0:02:23.240 --> 0:02:27.280 opening or mouth. The mantle organ adds new layers of calcium, 0:02:27.320 --> 0:02:30.919 carbonate and proteins to the mouth from below. As that 0:02:30.960 --> 0:02:35.000 new material hardens at the mouth, the shell grows, Spiraling 0:02:35.080 --> 0:02:39.600 coils form around the protoconch, which gradually spins around and around, 0:02:39.680 --> 0:02:43.800 becoming the apex, or uppermost tip of the snails widening shell. 0:02:44.400 --> 0:02:47.079 Depending on the species, the protoconch will either remain there 0:02:47.120 --> 0:02:51.280 permanently or break off at some point. Snail shells always 0:02:51.320 --> 0:02:54.080 coiled to the right or to the left. That's another 0:02:54.120 --> 0:02:57.520 thing that varies from species to species. Most snails possess 0:02:57.639 --> 0:03:00.080 right word pointing shells, but there are a few you 0:03:00.080 --> 0:03:03.480 whose shells orient towards the left, and in some species 0:03:03.520 --> 0:03:06.640 these shells can coil in either direction. If you were 0:03:06.680 --> 0:03:09.160 to cut open a snail shell, you've noticed several main 0:03:09.280 --> 0:03:13.280 layers in the cross section. At the surface, there's the pereostracum, 0:03:13.600 --> 0:03:17.600 a thin outer layer usually made with organic material. Below that, 0:03:17.680 --> 0:03:20.400 you've got a layer of hard calcium sitting atop a 0:03:20.400 --> 0:03:24.520 blanket of noker that's a resilient composite material better known 0:03:24.560 --> 0:03:28.200 as mother of pearl. One thing you won't find, however, 0:03:28.560 --> 0:03:32.200 is a network of nerves or blood vessels. Turtle shells, meanwhile, 0:03:32.240 --> 0:03:35.320 contain both. In most cases, the shells we find in 0:03:35.360 --> 0:03:38.680 these much adored reptiles are really networks of modified bones 0:03:38.760 --> 0:03:42.040 like ribs, vertebra, and pelvic elements that have been fused 0:03:42.120 --> 0:03:45.440 together and covered by hard plates. When a turtle's shell 0:03:45.520 --> 0:03:48.480 gets cracked, the body dispatches cells to try and repair 0:03:48.520 --> 0:03:51.720 the damage. Snails have a different method for fixing cracks. 0:03:52.040 --> 0:03:55.280 Calcium and protein secretions from their mantles can be used 0:03:55.320 --> 0:03:58.800 to help strengthen the damaged areas. Of course, having a shell, 0:03:59.040 --> 0:04:03.120 even one that can heal it self, does not guarantee safety. Ironically, 0:04:03.160 --> 0:04:05.640 a lot of nesting birds like to eat snails because 0:04:05.680 --> 0:04:08.480 of their protective shells and the calcium that they contain. 0:04:09.240 --> 0:04:11.920 To keep one step ahead of predators, many snails have 0:04:12.080 --> 0:04:15.320 seriously up to their self defense game. For example, the 0:04:15.440 --> 0:04:18.960 deep sea species Chrystomalin squire if um is covered in 0:04:19.000 --> 0:04:23.039 iron sulfide, giving the entire animal a strange metallic appearance 0:04:23.320 --> 0:04:27.159 and acting basically like battle armor. In fact, researchers have 0:04:27.240 --> 0:04:30.480 looked into the possibility of using this animal's amazing exterior 0:04:30.640 --> 0:04:36.240 to develop better armor for human soldiers. Today's episode was 0:04:36.279 --> 0:04:38.960 written by Mark Vansheny and produced by Tyler Clang with 0:04:39.040 --> 0:04:42.320 the kind engineering assistance of Ramsay youngt. For more on 0:04:42.360 --> 0:04:46.000 this and lots of other perhaps slimy but battle ready topics, 0:04:46.240 --> 0:05:00.120 visit our home planet, how stuff works dot com.