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Some interesting info on "nemerteans"

25K views 41 replies 18 participants last post by  RuRu 
#1 ·
I've been doing some research and looking through a lot of the photos and videos that people are posting of nemertean worms and it occured to me that the majority of the animals I'm seeing are not really nemerteans, but likely the flatworm Rhyncodemus sylvaticus. This species is widespread in the continental USA and has been found in Canada as well. It also predates on small insects so it more/less fills the same niche as the nemertean that shows up most often in the hobby, Argonemertes dendyi.

How to distinguish between the 2:

R. sylvaticus and A. dendyi are both variable in colour ranging from a pale yellowish to a brownish grey. They also reach approximately the same size - ~2 inches tops when stretched, generally around an inch when resting. Their appearance and movements, however, are quite different. The animal that has the pointed end and the "finger waving" movement is in fact R. sylvaticus. These worms lack the trademark nemertean proboscis and instead hunt their arthropod prey by simply "pouncing" on them, capturing them with an expanded cephalic hood and then immobilizing them with mucous, draining the fluids out and leaving a perfectly dry exoskeleton. Here is a photograph and a video of Rhynchodemus sylvaticus:

Rhynchodemus sylvaticus




Several members have/had the nemertean Argonemertes dendyi which has also been introduced to various tropical/subtropical areas including Hawaii and possibly Florida. These worms have a blunt rounded head and are generally more stocky looking than the flatworm. They move in a smooth gliding motion and hunt by firing the proboscis at the prey item and envenomating it. Feeding methods of the nemertean also leaves a dry exoskeleton. An easy way to identify A. dendyi (or rather to confirm that your mystery worm is in fact a nemertean) is to lightly prod the posterior end of the worm and see if it fires its proboscis to try and escape as shown in the video below.

Argonemertes dendyi




While I'm not sure if this information is too relevant (I'm not sure if there are any significant differences that could aid in eradication of one or the other for those who want them gone), I figured at the very least it could potentially help others identify their little monsters.
 
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#31 ·
So I've been doing some more research and it would appear that finding a creature that will reliably eat these flatworms might be a problem. A study was recently done on 2 species of hammerhead flatworm (Bipalium kewense and Bipalium adventitium) which found that they produce tetrodotoxin in their mucus, likely as a defensive as well as predatory mechanism. Apparently the egg cases are even more toxic than the worms themselves: PLOS ONE: Confirmation and Distribution of Tetrodotoxin for the First Time in Terrestrial Invertebrates: Two Terrestrial Flatworm Species (Bipalium adventitium and Bipalium kewense)

The little buggers that show up in vivs are actually capable of taking down insects far larger than springtails and fruit flies - here is a video of one of mine attacking a largish (~8mm body) yellow sac spider. I apologize for the quality, it was a quick vid snapped on my phone.

https://www.youtube.com/watch?v=IavswJ0l6zs

You'll notice that when the worm tags the spider the first time the spider struggles quite a bit then seems to suddenly stop, then the second attack results in only a slight struggle and complete paralysis of the spider. It appears that these flatworms also use some form of toxin, if not tetrodotoxin then probably a similar neurotoxin that is obviously quite potent. That would go a long way in explaining why most creatures that would happily munch on earthworms seem to ignore flatworms almost entirely.

I've so far had limited success with the larger isopods and a few random snail species but those were in small, controlled environments. In a large vivarium that has multiple food sources, I'm not sure how well they would work. In large numbers both of those can become pests themselves and, in larger containers, I find that once the egg predators are removed the worms seem to start appearing more frequently again. In larger containers they seem to persist unless I let the terrarium dry out or stop feeding them entirely, neither of which are practical solutions for enclosures with frogs and humidity loving plants.
 
#33 · (Edited)
I feel the chance of success would be quite low. Nematodes are significantly smaller than even newly hatched flatworms and far more delicate. Even tiny flatworms can anchor themselves and hold struggling flies, I doubt the trapping variety of fungus would have any effect. These fungi also seem to rely on detecting ascarosides which are molecules unique to nematodes so it's quite likely that they wouldn't even recognize flatworms as food - flatworms aren't even closely related to nematodes. I would imagine that the endoparasitic species would have similar problems in recognizing planaria as hosts - I feel it'd be just as likely to infect an earthworm as a planarian given that they seem to rely on chemical markers for prey detection and spore germination.

Furthermore, I'm located in Canada so I have no idea how importing specific species of fungi cross border would work, especially one that has potential as a biological pest control agent.
 
#34 ·
Yeah I can understand that. I was thinking more along the lines of the endoparasitic varieties relying on spore ingestion etc. but you are probably correct. I know we have to jump through some hoops at work shipping fungal material to Canada so I think that's the end all there. Keep up the good work though!
 
#41 ·
Hmm, I have had what I thought to be nemerteans in my various insect and snail vivs for at least a year and, unsurprisingly considering I keep bugs/snails, I was pleasantly surprised when I found them. Mine look mostly similar in body-plan to the ever present soil nematodes but are larger, brown and have an active hunting/striking posture that I haven't ever seen in a nematode. All of my vivs have been seeded both with soil/wood from old-growth redwood stands and soil from previous vivs so the microfauna should be about the same across all of my tanks. I am preparing to introduce mantellas into my 18x18x24 exo terra and am wondering if these nemerteans will eventually overpopulate. So far, I've never seen more that one at a time and my soil-arthropod biomass remains massive. Could it be that these are either not nemerteans, are a less invasive species, or are being kept in check by one of my other arthropods? Alternatively, is the explosive population and decimation of micro-fauna an exponential function that doesn't become apparent until a year or more down the line? If this is the case I might opt to put the mantellas on hold and build a new viv for them that I will seed species by species after some deli cup quarantine.
 
#42 ·
I've been doing some research and looking through a lot of the photos and videos that people are posting of nemertean worms and it occured to me that the majority of the animals I'm seeing are not really nemerteans, but likely the flatworm Rhyncodemus sylvaticus. This species is widespread in the continental USA and has been found in Canada as well. It also predates on small insects so it more/less fills the same niche as the nemertean that shows up most often in the hobby, Argonemertes dendyi.

How to distinguish between the 2:

R. sylvaticus and A. dendyi are both variable in colour ranging from a pale yellowish to a brownish grey. They also reach approximately the same size - ~2 inches tops when stretched, generally around an inch when resting. Their appearance and movements, however, are quite different. The animal that has the pointed end and the "finger waving" movement is in fact R. sylvaticus. These worms lack the trademark nemertean proboscis and instead hunt their arthropod prey by simply "pouncing" on them, capturing them with an expanded cephalic hood and then immobilizing them with mucous, draining the fluids out and leaving a perfectly dry exoskeleton. Here is a photograph and a video of Rhynchodemus sylvaticus:

Rhynchodemus sylvaticus




Several members have/had the nemertean Argonemertes dendyi which has also been introduced to various tropical/subtropical areas including Hawaii and possibly Florida. These worms have a blunt rounded head and are generally more stocky looking than the flatworm. They move in a smooth gliding motion and hunt by firing the proboscis at the prey item and envenomating it. Feeding methods of the nemertean also leaves a dry exoskeleton. An easy way to identify A. dendyi (or rather to confirm that your mystery worm is in fact a nemertean) is to lightly prod the posterior end of the worm and see if it fires its proboscis to try and escape as shown in the video below.

Argonemertes dendyi




While I'm not sure if this information is too relevant (I'm not sure if there are any significant differences that could aid in eradication of one or the other for those who want them gone), I figured at the very least it could potentially help others identify their little monsters.
Thank you so very much!! How do you get rid of them ? I have been trying forever. ?
 
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