What Is This?

[Kven]

Can anyone tell me what this is? It is in the rear of my tank on the overflow box. I woke up this morning to find this. Today is my clean tank and water change day—91 gal. It looks like a web in the design of the Tree of Life. This hobby requires so much knowledge; I am thankful for this resource.

 

[BristleWormHater]

I've had something like this in my tank before, here's a quote from @ISpeakForTheSeas

Given that it hasn't moved, my guess would be an Astorhizidan foraminiferan - I'm pretty sure I've seen them come up a few times now, but the last time I looked, there was very, very little info available (and I still need to finish reading through the few things I've found on them), so I haven't been able to confirm that.

Anyway, assuming that you have the same or a similar thing as the others I've seen before (which look suspiciously like a Radicula species), they would be harmless filter-feeders, and they typically disappear after a while.

For some pics you can compare with, see the figures in the first link below and (particularly) the plates at the end of the second link:
https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2022.1059616/fullhttps://www.researchgate.net/public...om_the_Andaman_Sea_Thailand_-_Taxonomic_notes

 

[208reef]

Looks like a spaghetti worm.

 

[ISpeakForTheSeas]

I've had something like this in my tank before, here's a quote from @ISpeakForTheSeas

Just to add to this for the OP (and assuming the thing is basically flat on the glass/substrate by the glass) - if it does move/disappear and reappear, it may be a very unique polychaete swarm; I haven't been able to ID the species yet, but sometimes these "tree" shapes that form in our tanks are tiny, tiny worms moving as a group in the tank.

Either way, foraminiferans or polychaetes, they seem to be harmless, and they're definitely neat.

 

[Michael71]

Looks like an Ansel Adams black and white to me... the rolling hills, rock outcroppings in the foreground...tree just over the rise of the hill lit by moonlight with hundreds of bright little stars in the background