GuyWalker1219
Reef Addict
Polyclad Flatworm (P.mopsus) The Clam Killer
by Guy Walker
© Copyright Marian K. Litvaitis, University of New Hampshire, 2005-2007
Phrikoceros mopsus, live animal
by Guy Walker
© Copyright Marian K. Litvaitis, University of New Hampshire, 2005-2007
Phrikoceros mopsus, live animal
Like a creature out of a 1950's science fiction movie it glides across a rocky terrain looking for its next victim to devour. This creature is truly a giant, a behemoth amongst its kind I am speaking of the polyclad flatworm Phrikoceros Mopsus the largest unwanted flatworm we see in the hobby and a known clam predator. In my research I could not find exact size ranges for this species but can say I myself have seen a 6" specimen and have heard reports of larger whether true or not I can not confirm.
The Polyclad Flatworm (P.mopsus) is a successful and stealthy nocturnal hunter believed not only to feed on Tridacna Clams but also small worms, crustaceans and snails making them a most unwanted guest in any reef aquarium. These flatworms hunt using chemo-sensory detectors that can detect and track their prey through the chemical compounds they release into the water column. They can kill and devour a clam over night I know this from first hand experience losing six prized clams before finding the culprits.
10 Clams in my 70g shallow reef
This flatworm can be hard to locate in a reef aquarium by nature they are designed to look like the mantles of clams in my opinion they look very much like the mantle of T. squamosa. They tend to hide in your rock work and unless moving blend in quite well making them very difficult to see. There are some signs though that can suggest you have one or more in your aquarium. Sudden and unexplained Clam death of course tops the list but there is another sign people do not normally think of. I was noticing dead snail shells at an alarming rate and had thought originally a mantis shrimp was the culprit and spent several hours looking for signs to no avail. Only after the clams started dying and I finally found on the shell of the last fatality three Polyclad Flatworms did I make the connection. In retrospect the snail deaths were in fact the first signs of the flatworms.
I have found once you have these guys in your tank the best way to remove is active hunting and or using bait and capture. If you have an unexplained clam fatality quickly remove and examine the remains if there is flesh left on the clam and flatworms are the culprit there is a good chance they could still be there. You can bait these guys using feeder clams in a fish trap checking often late at night this is how I caught the last one in my system. It has been over 2 years since I have seen any signs of Polyclad Flatworms.
I have always examined my clams very closely as well as placing them in my frag systems to observe and quarantine before placing in my tanks. I am not sure how I ended up with four Polyclad Flatworms in my tank I am assuming it was the purchase of live rock from a fellow reefer that explanation makes the most sense. If I ever found any sign of parasites in the past I would try and quarantine and treat according to type of suspected parasite. In worse cases I would freshwater dip I do not like this treatment and find it often speeds up or directly causes the clams death.
In March of 2012 I purchased a Black T. squamosa a clam I had wanted for some time and is a favorite amongst my current collection this purchase was made at a large aquarium expo. Being very crowded and me being in a hurry to see all I could at the show I neglected to examine the clam as well as I should have and upon returning home and closer inspection found a Polyclad Flatworm just below the mantle on the shell. At the time I had no quarantine or frag systems up and running and remembering my losses the year before I was very nervous about removing the flatworm and placing the clam in my display. My fear of contaminating my display and possibly losing other clams as a result pushed me to make a drastic decision. I decided to perform an experiment that had been on my mind for some time but had never tried. Not wanting to risk the death of any of my prized clams. I had decided to dip the clam in the commercial pesticide Bayer Advance complete insect killer that is commonly being used in the hobby for dipping SPS corals, all the while fearing I was going to kill the clam. During the dip the clam opened and expelled the liquid several times as if trying to clear its system of an irritant during this time I feared the dip was harming the clam but now believe it was trying to expel dying lifeforms wriggling around in its system. After 10 minutes I placed the clam in a bucket of clean tank water after a moment it opened fully I had to reach in and touch it so it would close and squirt out water I did this a few times to rinse out the clams system of the dip. I then placed the clam in my display and within seconds it was fully open and seemed very happy. Upon examination of the dip container I found the dead Polyclad Flatworm as well as a bristleworm and various unknown small crustaceans upon examination of the rinse container I found another bristleworm and a few more unknown small crustaceans. A month later I dipped a second Squamosa in the same manner it has been 10 months with no sign of ill affects with both clams growing rather well. Although I believe it to be safe it is not my intention to condone or promote the use of untested commercial pesticides in the aquarium hobby and can not guarantee the safety of anyone's livestock but I do feel it pertinent to share my experience based on the topic at hand.
Clam 10 months after dip in Bayer
Keeping Tridacna Clams can be fun and rewarding but as hobbyist we have an obligation to research and understand how to care for the livestock we plan to purchase. Far to many times have I seen new hobbyist purchasing clams on a whim without fully understanding how to care for them or even knowing if their systems are capable. Knowing how to inspect, recognize and treat common predators and pests is a good start and hopefully sharing my experiences can help someone who is looking to purchase a Clam make a better and more informed decision.
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