Foot full of water. With eyes.

 The local aquarium opened for the summer season a week ago. A mini-aquarium, one small room full of large, multi-species tanks, it houses animals and algae collected locally in the spring; they will spend the summer in a safe, comfortable setting, and be returned to their home in the fall.

I spent some time yesterday watching a moon snail plow through the sand.

Moon snail, Neverita lewisii, top view.

This snail is the largest of the moon snail family. This one's shell, visible only in part, is about the size of a baseball. As it moves about, the foot (the soft body, or mantle; it's a monopod, all one foot), flows smoothly over the shell and the sand, sometimes almost completely engulfing the shell.

On the front end (the propodium: pro- in front, podium- foot) there are two sharply-pointed tentacles, sensory organs that detect light and chemicals in the water. Off to the side, there is another structure, like a pipe with a black border on the rim. This is a siphon, which brings in water to flow over the gills between the inner part of the shell and the mantle, where the snail extracts oxygen from the water.

Face to face with the moon snail.

Watching the moon snail spread out, you wonder how it manages to retreat into its shell, or even if this is possible. It is: the foot is full of sinuses, hollow passages where water can be taken in to expand the foot, or expelled to shrink it down to the size of the shell cavity, a separate system from the siphon/gills arrangement. The snail can spread out up to 4 times the width of the shell; that's mostly water.

Rear view. The foot is wrinkled, as it expels some of the water from its foot.

If the snail is threatened, by a voracious sunflower star, for example, it retracts quickly into the shell and snaps shut the door, a flat, semi-transparent shield that fits the opening of the shell. It can't stay this way for long; it can't "breathe" while the siphon is locked inside.

The mouth is on the underside of the foot. Like those of other snails, it has the conveyor belt of sharp teeth, the radula.

~~~~~~~~~~

El acuario local abrió sus puertas, empezando su 2023 temporada, la semana pasada. Es un acuario muy pequeñito, apenas un cuarto lleno de tanques grandes; aquí animales y algas nativas, recogidas hace poco en las aguas próximas, pasarán el verano, protegidos y cómodos. En el otoño, los regresarán a los sitios de donde vinieron.

Pasé un rato ayer mirando un caracol luna mientras se deslizaba sobre la arena.

Foto: # 1: El caracol, visto desde arriba. Neverita lewisii.

Este caracol es el más grande de toda la familia de caracoles luna. La concha de ésta, envuelta en la carne (el pie), medía más o menos como un beisbol. El pie (también llamado el manto) fluye sobre la arena y su propia concha suavemente; a veces cubre casi por completo la concha.

En frente (en el propodio, desde pro- frente, podio- pie) lleva dos tentáculos puntiagudos, que son órganos sensoriales, captando la luz y los sabores de sustancias químicas en el agua. A un lado, hay un sifón, que parece un tubito con el borde marcado en negro. Aquí entra agua para pasar sobre las branchias ubicadas entre el manto y la superficie interna de la concha, permitiendo la extracción de oxígeno del agua.

Foto #2: Cara a cara con el caracol.

Viendo como se extiende el caracol, parece difícil que pueda retraerse por completo dentro de la concha. Pero lo logra porque el tejido del pie está lleno de canales llamados senos, donde entra el agua para aumentar el tamaño del pie, o de donde se puede exprimir, para que el animal quepa dentro de la concha. Este sistema no forma parte del sistema del sifón/branquias. El caracol luna se puede extender hasta a 4 veces el diámetro de la concha; la mayor parte de esto es agua.

Foto #3: Visto desde atrás. Se ve arrugada la parte final, de donde se ha exprimido algo del agua.

Si el caracol percibe alguna amenaza, como por ejemplo la estrella girasol, se mete rápidamente dentro de su concha y cierra la puerta, el opérculo, que es una placa semi-transparente del tamaño y forma de la apertura en la concha. No se puede mantener por mucho tiempo así, porque esto también cierra el sifón, impidiendo que el caracol pueda obtener oxígeno.

La boca no se ve en estas fotos; está en la planta del pie, y contiene la rádula con muchos dientes, como otros caracoles marinos.

Welcoming committee

For New Year's Day, I posted a photo of a brand new, freshly hatched, pinhead-sized Leafy Hornmouth snail, just starting out on his adventure. This is the backstory.

It started with the small kelp holdfast I brought back from the beach in November. It came with its own cargo of crabs and worms and starfish, but there was a small blank space on the inner side of the clamshell; here, the pair of big snails* in my tank chose to anchor their latest batch of egg cases.

The inner side of the clamshell, as it is today. Much-nibbled-on kelp "roots", and the egg cases at the bottom.

The first of the baby snails started to emerge from the cases a couple of weeks ago. I was on hand to photograph the "birth". So were some other observers, with more ominous intentions.

Three open egg cases. The siphon tip of the latest baby peeks out the exit hole of one.

Several snails hatching at once, at the beginning of the escape. Several egg cases still have their plug in the escape hatch. (Top two on the left, for example.) But look carefully at the background!

Waiting for dinner to be served. Flatworms are always hungry!

There were two flatworms, both very tiny, as flatworms go, humongous in relation to baby snails. One was green; I'd seen it before, but this purplish one has only showed up for the hatching, and has never been seen before or since.

The smallest of the black-clawed crabs, still living in the holdfast.

Against the back wall of the clamshell, too tiny to see without a lens, I found a colony of green anemones. Looking again later, I saw that one had a snail in its mouth.

Watch the holdfast for a couple of minutes, and somewhere among the roots, a worm will poke out his head. There are a dozen or so living here.

Polychaete in his tunnel made of a glued fold in sea lettuce. Tiny, but those jaws will gape as wide as the belly of the beast.

Out searching for food. The tail never leaves the burrow, but he can stretch the full width and height of the holdfast colony.

The brittle stars seem to have disappeared, which would be a relief to the snail parents, if they were of the type to fuss over their offspring. The other two stars have been deported to the shore where they came from, for crimes against snaility. (They were eating the tank cleanup crew; they would have had these babies for appetizers.)

Mortality rates are high in the intertidal zone, especially for the young. One of those egg cases would have started out with about 50 eggs; less than half would survive to hatch. And of the hatchlings, depending on where they emerge and the predator load, anywhere from 50% to 99% will die within the first few weeks.

Observations in San Juan Islands, Washington show that a newly hatched N. lamellosa (Related to my leafies - me) has a 1-2% chance to reach 3mo of age.  An individual reaching 3mo has a 35% chance to reach 1yr of age.  Older, larger, individuals have a 40-60% chance to survive through subsequent years.  Spight 1975 Oikos 26: 9. (From A Snail's Odyssey)

My baby snails, those that made it past the welcoming committee, hurried out of the holdfast to hide in the sand.

On his way.

Zooming in. Siphon to the left, leading the way. Within a few seconds, he had ballooned off the holdfast root, washed away in the current to a "safer" place.

Even out of the holdfast, there are dangers. Hermit crabs. Even the tiny hermit crabs. Shore crabs. Anemones everywhere. Any of these will relish a tender baby snail hors d'oeuvre. The ballooning snail burrowed down into the sand as quickly as he could.

But there are worms down there.

Three times, I've seen a baby on the glass, high above the sand, out of reach of all but the climbing hermits. Good choice. They may survive.

Infant snail, above the water line, surrounded by his own body bubble. Taken through the glass, against the light, which shines through the yellow button at the tip, and shows the ridges on the shell. The dark spot is the operculum, which closes the shell when the snail is resting.

*The parents were Mike and Tillie, Leafy Hornmouth snails (Ceratostoma foliatum). They have since been returned to their home beach, since my visits to the winter shores weren't providing enough juicy barnacles to keep them fed in the tank.

Jugs full of eggs

Two years ago, in April* of 2012, I brought home a clamshell that contained, under a crowded community of snails, hermits, worms, and more, a set of little brownish jug-like things. Eventually, commenters identified them, tentatively, as Murex snail egg cases, possibly trophon snails.

"Jugs" Photo from 2012.

And now, the mystery is solved! Yes, they are trophon eggs.

Remember the two-toned trophon snail that has been eating barnacles in my tank? I brought her** home a companion from our last trip to the beach; another trophon, slightly smaller.

For several days, they've been circling each other, warily, approaching then backing off. Neither showed an inclination to bury themselves in the sand, or eat another barnacle. Today, only the newcomer was visible, though, until Laurie found the other hidden behind an abalone shell in the back of the tank in the evening. She was busy; laying eggs, in a sort of grid pattern stuck to the glass.

After an hour or so, the newcomer joined her. She stuck herself to Snail #1's shell and waited until she had finished.

I rigged up some lighting, and a mirror behind the tank, and took their photo in the mirror, since I couldn't even get the camera into the small space.

More "jugs", with their bottoms glued to the glass, facing us.

Snail #1 is finished, now. She's moved to the bottom. She looks skinny, as if the shell were now too big for her. Snail #2 is twisting herself around beside the egg cases; getting ready to lay her own, maybe?

*It looks like April is the egg-laying month for these snails.

** I wrote then, "*Most snails are hermaphrodites, but these ones have separate sexes. I don't like calling a conscious critter an "it", so I've opted for calling this guy a male." I guessed wrong. She's definitely female!***

***She needs a name. I can't keep saying Snail #1, #2.

Snail, out hunting

A week or so ago, I wrote about a two-tone trophon snail from Boundary Bay. At the time, I had been trying to get a photo of the siphon he extends through the canal at the tip of his shell, but he wasn't co-operating.

He finally showed up near the wall a couple of days ago, and let me get a few photos.

Trophonopsis orpheus, on an abalone shell against the wall. The tip of the siphon is just visible at lower right.

Climbing over a blade of eelgrass. The eyes are near the tips of his tentacles. The siphon is visible, extended through the siphonal canal.

How much he sees with those little eyes is debatable, but his main guidance system is the siphon. He's "breathing" in the water through the tube, and also "smelling" his way. A few hours later, he had found the barnacles on a stick on the far side of the tank, and was busy emptying the biggest.

And now he's back buried in the sand, digesting.

Bi-coloured snail

Sometime last summer, a snail I hadn't seen before came home from Boundary Bay with me, hiding in a bag of greens for my hermits. He* was small and dark, slate grey and brown, sort of whelk-shaped, nondescript. Nothing to write home about.

I added him to the tank with some trepidation; the whelks and their ilk are usually predators, and sometimes very hungry. I kept an eye on him, and on the possible food sources in the tank; there are a couple of clams, some mussels, always a few barnacles. When I do a thorough cleaning, I comb through the sand. The clams are still there. The mussels are bigger than they were. But the barnacles I've added just a bit ago are now empty shells.

The snail eats barnacles. Nothing else, it seems.

Barnacles are easy to come by, in quantity. He can stay.

Last August, heading up out of the sand.

He spends much of his time like this, half-buried in the sand, barely moving. Then for a day or three, he surfaces and goes looking for another barnacle, glues himself to the unfortunate choice, and leaves it gaping open and empty. Back to the sand to sleep it off.

About a month ago, on one of his food runs, I noticed how much he had grown. But the new shell seemed almost to belong to another snail entirely. It was almost white, in sharp contrast to the old slate-grey shell.

The white is dirty, now, algae-encrusted. But the divide is still there.

And the new shell is more ridged than the old section, possibly because the snail isn't being rolled around by fast currents.

He's a Corded trophon, Trophonopsis orpheus, aka Boreotrophon orpheus, a subtidal resident, rarely seen above the low tide line. I have only seen one before, an infant, newly hatched from the egg case.

Baby trophon, April, 2012. A few millimetres long. New, sharp sculpturing.

It looks like the dark grey colouring came from the shore where the snail was living, or from his diet. (Black barnacles?)

These snails are distinctive for their long siphonal canal, the tube that protects the siphon through which the snail "breathes" and finds prey. A good idea; the siphon is the most vulnerable part of this type of snail, sticking out well in front, soft and inviting.

Little Nassa, leading the way with her small, unprotected siphon. 

Trophon bottom, showing the siphonal canal. The opening and exit are just visible.

Flipping back the operculum (that reddish lid) to extend the foot.

Spotted orange and white skin of the foot. The siphon canal extends to the right, the direction of travel.

Muricid (whelks and their ilk - rock snails) shells are variably shaped, generally with a raised spire and strong sculpture with spiral ridges and often axial varices  . . .
Many muricids have episodic growth, which means their shells grow in spurts, remaining the same size for a while (during which time the varix develops) before rapidly growing to the next size stage. The result is the series of above mentioned varices on each whorl. (From Wikipedia)

The ridges, in the photo above, go top to bottom; the varices (sing. varix) go left to right. The shell building continues; it has turned the corner and started on the next lap, which will be bigger than the one just added. The raised lip where the shell turns is a varix.

The snail had been sitting on the pump for a couple of days, so I brought him out for a photoshoot. He didn't seem to mind sitting on plastic foam, and started to roam. I waited, hoping for him to extend the siphon, but there was no sign of it, probably because he was out of water. He's back in the tank now, and has buried himself again, without eating the last two barnacles I've brought him. Sulking, probably.

*Most snails are hermaphrodites, but these ones have separate sexes. I don't like calling a conscious critter an "it", so I've opted for calling this guy a male.