Flatworm - Acoel Planaria

[jthomps123]

Update on my red/rust flatworms. They still continue to accumulate in my sump in epic proporations, but have been invisible in the display tank. I attribute this to my green mandarin, who is extremely fat.

[Craig Manoukian]

Great news, about the Mandarin of course!

[tomshannon]

Originally Posted by leahski

so you recommend that they need to be disposed of? i wasn't sure if they really posed any threat to my tank since it will be softies and a goby...no acro or sps.

Hi Tori,

In answer to your question(s), and given that you have Convolutriloba acoels (rust/red flatworms) they don't pose a threat to your tank despite conventional "wisdom". I answered a similar question on another forum site but will repost it here as well:

Bear in mind that I am only speaking on behalf of Convolutrilobids...

1) Will they damage my corals?

Absolutely not. Contrary to popular belief they do not feed on coral tissue, nor do they obtain their algal symbionts from corals, through consumption or otherwise. The acoel symbionts are "green" prasinophyte algae, most likely Tetraselmis sp. Corals, on the other hand, harbor "brown" dinoflagellate algae of the Genus Symbiodinium. Convolutriloba feed on tiny crustaceans or crustacean larvae, rotifers, and other tiny invertebrates; not diatoms, as is commonly assumed. They are ambush predators.

2) Will they eat something beneficial?

Depends on what you're calling "beneficial". Will they eat the pretty macro-stuff in your tank? No. They will, however, compete with other critters in your tank for resources such as copepods, Artemia, etc., but no more than any other carnivore/omnivore. The main difference that becomes apparent rather quickly is that their population growth responds much faster to changes in resource (food) availability than that of larger "desired" invertebrates and fish. Please note, however, before worrying that they will starve out your corals and wipe out your copepod populations, that their numbers will fall in response to resource scarcity just as quickly as they rose in response to resource abundance.

3) Will they produce toxins when they die?

No, but they will if they are killed. When food is scarce the acoels will begin to starve, and just like most other animals, starvation leads to rapid weight loss. The Convolutriloba cannot survive indefinitely on algal photosynthesis alone. Before these animals die from starvation, they are so small and depleted that upon their death their bodies contain little or no toxin. When the acoels are killed, however, be it by chemical warfare, salinity changes, temperature changes, predation, maceration, or squishing, they will release a potent toxin and make life pretty miserable for the other tank denizens... Food for thought: the death of a medium-sized tang, if unnoticed, will cause a spike in a tanks ammonium levels and make everyone's lives just as miserable; but you never hear anyone preaching to KILL KILL KILL all medium-sized tangs.

4) They're ugly & icky.

So's my aunt. She's even got a moustache, but I'm not about to condone her eradication or banishment from the biosphere. Beauty is in the eye of the beholder.

5) Reef wisdom says they will block sunlight from corals.

Reef wisdom ain't as wise as it thinks it is . For the most part, Convolutriloba don't like hanging out on coral; corals sting. They are more often found along the bottom edges and corners of tanks, on live-rock outcroppings, or just outside of shadows on the substrate. This isn't to say that they never climb onto corals (certain Sarcophyton capitulae seem to attract them at times), but unlike some Waminoa species, it's not their usual modus operandi.

6) A year or two is too long to wait for most hobbyists.

That is how long it usually takes for a population to die off on its own. By no means does this imply that one will have gazillions of Convolutriloba for two years, then suddenly none. Again, the populations wax and wane according to resource availability. The best way to keep the numbers in check is to know your system; know how much food is enough to keep everything in your tank happy and healthy; and don't feed it any more than that. By carefully monitoring the addition of food, everything in your tank benefits and you won't experience large-scale population explosions of Convolutriloba. Eventually they'll just slowly wither away to nothing .

[Craig Manoukian]

Very good information Tom!