The Meandering Moon Snail

One of my field sites, Fossil Point, is outside the main channel of focus for my study. Its in the main channel of Coos Bay, not South Slough. I'm keeping this site because its really close to the mouth of the estuary and also has very high marine influence (somewhat of a replicate for my marine site). I'm not sure if I really need this site in terms of data collection, but its a cool spot so I'm keeping it for the time being. Once you get beyond the smell of the Dairy Queen (just down the street) and way out on the mudflat, there's always an unexpected find. If you recall from a past post, last time I was out here some clammers asked me about the i.d. of a moon snail. Well, it was still here this time round, making its way, slow as a snail, to deeper water. Ok, so there's a chance that it wasn't the exact same snail, but I think it was, guarding my transect line. Its large foot was extended like a sail, reaching into the strong shoreward breeze. It was making no effort to concel itself underneath the plentiful eelgrass beds, and it wonder if its brazeness was do to its gigantic proportions. Its so incredibly huge that I wonder what birds or other predators would be able to eat it. After photographing this beast of a snail from every possible angle I helped it down to the channel edge where I presume it was headed. Here's a chunk of a short storythat my mom wrote which features the moon snail:


"It’s all about survival”, says Bill, as he slowly stretches back to a standing position. “Competition. Reproduction. Predation. Moon snails are a good example.”
He peers into the muck of the nearly drained lagoon. “Moon snails are in the same phylum as most of these bivalves, mollusca, but they’re in the gastropoda class. That means ‘stomach foot’”. He looks around, and then squishes further into the disappearing lagoon, boots sucking against the suction of the mud. He walks back towards us carrying a rubbery band that looks like a small inner tube, and holds it up for everyone to see. His voice slows: "This is the egg collar of a moonsnail."
The sunlight sparkles the life ring like diatoms glimmering in a honeycomb incubator. Bill’s voice softens and slows, "At high tide in mid-summer, these egg cases will crumble, releasing thousands of eggs." The class straggles to the edge of the stream following Bill.
Nobody speaks.
He lays down the collar, and begins to prod gently around a round protuberance in the sand, then more quickly digs into the gravel around it. The snail moves like a softball in a very slow pitch, trying to dig itself down, but Bill is too quick. He holds it aloft on his trowel, cupping it with his other hand. The foot of the snail jelly-rolls underneath, slimy and translucent and enormous, extending beyond the circumference of the shell. Bill’s voice is solemn as he points to the gelatinous mass: “The foot motors the snail along, and it digs to avoid predators and unwelcome events such as this.”
The class is in a trance.
Bill holds up the shell. “Moon snails are carnivores. This thing,” he slowly turns so everyone can get a good look, “will hunt down molluscs, like clams, snails and mussels, and surround them with their foot, this gooey underneath part.” He’s talking faster now. “Then it drills a beveled hole through the shell of its prey with its radula, inserts its proboscis, and yum, yum, yum…”
Sophie winces, holding up a clamshell with a hole in it. “Is that what happened to this poor clam?”
Bill walks peers at the clamshell. “Yup, you can always tell whodunit by that beveled hole. That’s the moonsnail’s signature. The drilling can take hours. So if the prey escapes, and is recaptured, the moon snail will drill in a new place. If you see shells with several holes, that’s probably what happened.”
The night of the living dead. This round, benign shell, with no visible teeth or horns or poisonous antennae, is a predator. It consumes almost everything we've observed.
Sophie asks the question I’ve been thinking, “But why isn’t the moon snail a bivalve? Why is it round instead of flat? What makes the shell go around like that?”

“It’s because of something called ‘torsion’, says Bill. “When it’s growing, one side of the larvae grows more quickly than the other, and twists around 180 degrees from the rest of the body. And look at the shell – it’s much smoother than those oysters, you see, so it can burrow down into the mud.”

But Bill’s snail has other business. Thousands of tiny eggs are pressed together with particles of sand, wrapping its shell in a rubbery collar. Bill gently strokes off the sandy outer layer, and the egg casing is exposed in a thin, moist wrapping.

It is like seeing the Holy Grail.
Without a word, Bill turns away from the class, digs back down into the streambed, tucks the shell back in place, and covers its sides. The moonsnail oozes down into the mud and out of sight. cc Melody Hessing

p.s. I saw an egg casing as I was walking back to shore, perhaps this guy had chosen my site as a good spot for disposal of its progeny.