Can anyone idendify these small growing things?

[brainologist]

We've recently noticed these strange flora growing in our planted tank. The tank's been up and running for about 2 months now, and this is the first time we've seen these things. I don't know whether they're plants or animals. They're also very small and hard to take pictures of, so forgive the poor quality of these images.

Can anyone tell us what these are? Are they dangerous to the fish? Should we just suck out the ones we can see, or do we need to do some more extensive cleaning?

The organisms in question are whitish anemone-looking growths that attach to the driftwwod, glass, and plant leaves. They are about 5mm (~ 1/8 inch) long, have a single, thickish stalk that serves as a base, attached to which are 5 'arms' projecting radially from the top. Each arm is itself a little less than 5mm. We have 2 Otocinclus sp., which do not seem interested in eating these organisms. Neither do the blue tetras (Boehlkea fredcochui).

Other info (but hopefully no red-herrings!): Tank parameters: pH: 6.4; NH3: 0ppm; NO2: 0ppm; NO3: < 5ppm. We do ~20% PWC every week. Two weeks ago we added peat pellets to bring our pH down (it had previously been consistently 7.2) because we are looking to get some blue rams.

Following are three pictures (attached). The first is a regular view of three of these on the driftwood. The second is zooomed in on one of those three. The third show another attached to the glass, where you can see the radial arms. If these are not helpful, I will try to get some better pictures when the camera recharges.

 

[plecoperson]

They look like hydra, and a little like that neuron (or whatever it is) in yer avatar!

 

[Purrbox]

Definately Hydra. They are not dangerous to adult fish, but will feed on any tiny fry they catch.

 

[brainologist]

Hydra, huh? Guess I better put in a call to Hercules. Not likely to get any fry in this tank, so I won't worry too much -- just pluck them out when they become unsightly.

Another question:
While doing the PWC tonight, we uncovered a long white worm. I don't have a photo because we vacuumed it out just as soon as we saw it. It was about 1-2" long, and was swimming vertically (length of worm was up to down). It was swimming by waving rapidly in a sinusoidal / sigmoidal kind of way. My girlfriend swears she saw one just like it two days ago -- and that one was snared and eaten by a Hydra.

I've searched the forums for a similar description, but didn't find anything. The two times we've seen these, they've been swimming; never crawling on the glass like planaria are want to do. I'll stay vigilant and try to get a photo. But until then, speculations? Any ideas?

 

[Purrbox]

Not sure of your terms for the worm's movement. Do you mean that it was wiggling in sort of an S shape? I get similar worms in my tanks from time to time, although mine are only 1-2cm long and 1mm diameter. If you've got the same thing, then they're harmless and a sign of good water quality. I don't remember the name of them off hand.