what is this white segmented mass?

[NanoCat]

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I've been keeping an eye on this strange white "thing" over the last two weeks and now it seems to be growing and spreading. Anyone know what this is and what a good course of action might be.

It's hard to describe. White, sessile, seems to have multiple segmented "arms" rooted to a central base. One of the patches (on the right) also has small oval masses... (eggs maybe? Seems odd).

It's a mystery to me. Can't figure out how to describe it to get any good info through google searches.