How to deal with Pyramidellidea snails

Pyramidellidea snails, commonly called “pyramid, pyram or rice snails” are one of the most common pests/parasites that keepers of Tridacnid clams will come across. There are over 8000 species of pyramidellid snails throughout the oceans, and as a group, these ectoparasites have been reported to feed on bivalves, gastropods, polychaetes, echinoderms and polyplacophorans (Robertson & Orr, 1961).



Pyramidellids are primarily nocturnal and tend to stick close to their host. They feed at night using their proboscis to pierce the host’s flesh and feed on the host’s body fluids. According to Robertson & Mau-Lastovicka (1979), some species can, and will, feed on unnatural hosts so there is the possibility of pyrams found on snails moving over to bivalves and visa versa. In small numbers, pyram snails can be tolerated by the host and seem to do little damage. Pyrams, however, multiply very quickly. Their egg masses can contain hundreds of eggs. These eggs hatch after about 15 days, become sexually mature at about 45 days, and have a life cycle of about 120 days. So, two pyrams today can become hundreds in a month and thousands in a few months. In larger populations these parasites will quickly weaken the host, leading to its death if left unchecked. Before placing any new clams or snails into your aquarium, inspect their shells well, looking all around the shell for these 1/8” snails and also look for clear jelly-like egg masses. If you find either, thoroughly clean the shell with a soft brush (as described below). Ideally, it’s best to place any new additions into a quarantine tank – whether they have pyrams or not. If pyrams are introduced into your display tank, it can be a long and tedious ordeal to completely eradicate them.

So how do you know that the snails you have are pyrams and not harmless rissoid? If you have a good magnifying glass or microscope, you can look at the orientation of the apical shell whorl. In pyrams, it’s perpendicular or turned 90 degrees, whereas rissoids' whorls are all the same (Shimek 2006.) Or you could say “those little white snails are getting a little too friendly with my clam, I bet they’re pyrams! Better get rid of them.”

What if you already have them in your aquarium? All is not lost. Take a deep breath, roll up your sleeves and gather some supplies.



The above photo is your pyram eradication kit. As you can see it contains a soft toothbrush for brushing around the shell's edge and the clam's byssal opening to avoid damaging any flesh. Use a stiffer brush for scrubbing the middle of the shell where you won’t be in danger of contacting the flesh, and a few pointy objects for getting into nooks, crannies and crevices where the brushes can’t reach. I like kabob skewers for this purpose because they are disposable. I’ve used nice sharp kitchen utensils before, but they end up getting me into the dog house with my spouse. It's also adviseable to find a well-lit area where you don’t mind splashing a little tank water or flicking snails in it.


Okay, so now you’ve chosen your weapons, what about your plan of attack? Remember that pyrams are nocturnal so we are going to use this to our advantage. About an hour or two after all lights are out in the aquarium the pyrams will start to come out to feed on their host. Fill up two containers that are large enough to hold the clam with aquarium water. Gently grab the clam and turn it so that the mantle is horizontal and slowly lift it out of the water. You never want to remove a clam from the water – especially a large clam – with the mantle pointing up (vertical) because clams can not support their mantles while out of the water. Bring the clam over to your work area, and give it a good once over to see how many pyrams you are dealing with.





Egg mass


Now grab the soft toothbrush, and with the clam’s mantle horizontal and facing slightly down, start brushing all along the shell's edge. Brush away from the clam so that the snails do not land back on the shell or go into the mantle cavity. Make sure you get into every nook and also brush areas that don’t appear to have pyrams because the egg sacks and newly hatched juveniles are nearly impossible to see. Use the pointy object of your choice to get clean out any areas the brush can’t. Continue all around the shell's edge to the byssus and up the hinge ligament. Then brush the middle of the shell with the toothbrush or the stiffer brush. When you are convinced you removed them all, turn the clam over and repeat on the other half of the shell. When you are finished, place the clam into one of the two containers of tank water you filled earlier and quickly brush the shell again to remove any eggs or snails you loosened earlier. Then place the clam into the second container.

Before you place the clam back into the display, if the clam was on the sand, scoop out the substrate from where the clam was to remove any pyrams that might have been hiding there. When replacing the clam back into the aquarium, lower it into the water slowly with the mantle still horizontal until fully under water, then turn the clam so the mantle is facing up and gently rock the clam back and forth to release any air that might be trapped under the mantle cavity (burp the clam). Another trick you can use is to fill a small Tupperware™ container with sand and place that in the aquarium and then place the clam in the container.

Why go through all of this? Because no matter how hard you tried, you missed a few snails and or eggs (trust me). So, for the next four to six weeks you will need to repeat this cleaning routine two to three times a week, discarding the substrate as well. Even if you don’t see any snails, do the whole routine. After six weeks you can slow down to once a week for another six weeks. And then from there periodically inspect the clam. I know, it sounds like a lot of work. All the more reason to set up a quarantine tank; everything you add to your tank may harbor unwanted pests.

Possible Predators


There are a few fish like the Six-line wrasse (Pseudochellinus hexataenia), the Four-line wrasse (P. tetrataenia) and the Yellow Coris wrasse (Halichoeres chrysus) that may eat pyrams, but at their best, these fish will only control the population, not eradicate them. Remember, pyrams are nocturnal (active at night) and wrasses are diurnal (active during the day). So you may find a fish that eats some, but if you’re depending on one of these fish to eradicate them, in my opinion, it’s not going to happen.

With any luck, you'll rid your tank of these pests forever.

Great thread Chris, now time to get the word out.....

Can clams be dipped in any solutions out there??

I wouldnt recommend it. If your thinking of dipping them to get rid of pyrams you have to remember that snails and clams are both mollusks and anything that would kill pyram snails would also kill the clam.

I thought this but a friend didn't believe me, after dipping in flatworm exit and killing a couple of clams..

SHEET, CHRIS,
are these pyr snails? can't get any better pics.
found them in the middle of the day. pyrs are nocturnal, though? one was on the shell high up.
should i see them move when removed from the water? none did.
could not tell if anything was alive in the shells.they looked whiter in person than in these pix
assistance needed. the maybe infected clam is the one i cut off. he looks fine now, but is isolated. the one that had been shading him also looks fine.

Yes they are. The only way to tell (for us hobbyists) is to look at the first whirl of the shell and luckily in the last pic you posted, the snail on the left is positioned just right so you can see that whirl.

Your going to need to follow the directions at the top of this thread to get rid of them.

so, now that i know the bad news, any assistance you can offer is great:
i assume i have to take and treat all the snails? should i isolate each one in a small tupperware container? that's where the crocea the pyr came from is now. no sand, just its rock.
do i need to remove it from the rock in order to effectively scrub?
do all of them clams need to have a clear shell at the bottom?
should i set up a separate qt for them?
what would you do if you were a week away from setting up a second tank?
why are the snails on the move in the daytime?
last for now, why does the clam look fine now? see pic.

i assume i have to take and treat all the snails?

Im guessing you meant clams? if so yes, they should all be inspected.

should i isolate each one in a small tupperware container?

it would help to have them all in a container like that filled with sand so the clams can be inspected and cleaned often and the sand can be replaced after every cleaning.

that's where the crocea the pyr came from is now. no sand, just its rock.
do i need to remove it from the rock in order to effectively scrub?

What size rock are we talking about? A small size rock that you can easily clean around might be ok but if it is that small it should be easy to remove and with it gone it will make life a lot easier.

do all of them clams need to have a clear shell at the bottom?

Not necessarily but you do need to be able to clean and inspect them easily as needed

should i set up a separate qt for them?

No, the pyrams are already in the tank right? IMO keep them in the stable, established tank and be diligent in removing the snails.

what would you do if you were a week away from setting up a second tank?

Set up the new tank and let it cycle and deal with the pyrams in the old tank.

why are the snails on the move in the daytime?

even a crackhead gets up early sometimes

last for now, why does the clam look fine now? see pic.

why does it look fine? pyrams slowly suck the life out of clams. clams can deal with them in small numbers but when the population gets larger it takes a toll on the clam.

mucho thanks for all the horrible info. yes i did mean clams. i will treat the ones i can for cut off and put in containers, probably 3-4, and keep them separate from the others. basically none of the rocks they are on are smaller than an inch. the plan for the second tank was to move rock into it along with the critters. my thinking now is, since i need lots of bottom space for the tupperware/sand/clams, i need to move non-clam stuff into the new tank, with some water and keep the majority of things where they are.
how long can the snails exist without a host?
seems as if i'm in for a long haul. that clam has been in the tank at least a month, so i'm pretty sure all or nearly all have the bstrds.
arghghrhghghhhhh

Paul which clam did these come in on?? And where did you get it?

snails are on a clam from lareefs, but who knows if that one was the original one infected.

how long can the snails exist without a host?

There life cycle is about 120 days but how long they can go with out feeding i dont know

Man it is a crapshoot on what clam they came on, especially if they have been in the tank a month now.

scrubbed it and found only one other snail. chris, your pics show the mantle extended somewhat. this clam closed up pretty dam tight. flesh was completely gone, so i dont really understand the pics you have up here, either, i don't have that much white area on the clam. what's the orientation of the clam? where are its ridges [scutes??] do i see the mantle of a derasa in the pic with the eggmass?

btw, i used a flashlight on all the other clams. if there was a serious infestation, wouldn't i see 1 or 2 on the clams now? didn't see anything. i still understand it's bad and serious, but maybe not suicidal bad?

I think Chris's clam pic's are with the clam open because his clams were huge. Once they get to a certain point they can't close up 100%.

aaah skinz, that explains it. now at 4 a.m i looked and saw no snails on clams and the same at 6:30, shouldn't i see something on one shell out of 10 at night if these bstrds are nocturnal? does this mean i am just beginning the troubles? just confusing and frustrating!!

Originally Posted by shmoliken

chris, your pics show the mantle extended somewhat. this clam closed up pretty dam tight. flesh was completely gone, so i dont really understand the pics you have up here, either, i don't have that much white area on the clam. what's the orientation of the clam? where are its ridges [scutes??] do i see the mantle of a derasa in the pic with the eggmass?

The photos i used are of a squamosa and they are close ups, top down of the scute. The mantle was fully withdrawn into the shell but the shell was not fully shut. FWIW i could pull that clam all the way out of the water and it wouldnt even withdraw its mantle sometimes. Clams dont always close up tight.

Originally Posted by shmoliken

btw, i used a flashlight on all the other clams. if there was a serious infestation, wouldn't i see 1 or 2 on the clams now? didn't see anything. i still understand it's bad and serious, but maybe not suicidal bad?

You could go a few days or weeks without seeing any new snails but that doesnt mean they are not there. If you caught them early there may only be a few adult snails right now but if you dont clean and inspect often and one single snail gets past you and lays eggs, in a week you could have hundreds.

Originally Posted by shmoliken

aaah skinz, that explains it. now at 4 a.m i looked and saw no snails on clams and the same at 6:30, shouldn't i see something on one shell out of 10 at night if these bstrds are nocturnal? does this mean i am just beginning the troubles? just confusing and frustrating!!

Just clean and inspect them 3 times a week. You need to stay on top of it. Dont let it stress you out, just make it part of your routine for a while now.

Originally Posted by chris&barb

The photos i used are of a squamosa and they are close ups, top down of the scute. The mantle was fully withdrawn into the shell but the shell was not fully shut. FWIW i could pull that clam all the way out of the water and it wouldnt even withdraw its mantle sometimes. Clams dont always close up tight.



You could go a few days or weeks without seeing any new snails but that doesnt mean they are not there. If you caught them early there may only be a few adult snails right now but if you dont clean and inspect often and one single snail gets past you and lays eggs, in a week you could have hundreds.



Just clean and inspect them 3 times a week. You need to stay on top of it. Dont let it stress you out, just make it part of your routine for a while now.

i will do me best. thanks for all your answers.
a few more questions:
should i see snail living tissue inside the shell? should they move around outta the water?
i was planning a tank breakdown and move of most of my critters into a bigger tank. THIS WEEKEND. what are your thoughts on that with this new ugly situation??
both tanks were going to be plumbed together in the basement.