What is growing on this oyster?

[Lyvric]

Hand is not mine. Found it in a reef tank. See attached images please.

 

[Speaker73]

Sponge


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[vlangel]

Yes, it looks like a sponge to me as well. You might want to remove it so it does not smother the oyster.

 

[Rzimmerman]

what's growing

what's growing

Did water squirt out when you took it out of the tank? It looks like a Urochordate (sea squirt). It has an odd shape for one but the fact that it looked so different in and out of the water makes me wonder about the sponge description. I would say sea squirt if water came out at once or a sponge if it came out more slowly. Either way, they are both filter feeders so they would be competing for algae.