Wierd wormlike appendage

I have a 7 month 12g Nanocube with 2 hairy mushrooms. Last night, a long, brown, slender "thing" was coming out of one shroom. It broke off and dissolved. About an hour later, the other shroom emitted one. It would grow some 4-5 inches before breaking off. The water parameters are fine. So, what are these things? At first glance, it resembles a tentacle.
Thanks in advance
 
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