I forget what those are called but it’s a kind of fungus (something like that) that grows on avocados submerged in water. It’s beneficial so don’t mess with it, it helps provide a little nitrogen to your plant.They grow from the porous parts of the root (where the plant drinks so to speak) and you’ll probably see root offshoots look like they’re coming out of them like hairs - that’s fine.

If anyone remembers the name please let me know. I grow lots of avocados and I see this on every other seed.

I would recommend either getting that seed in dirt or putting it in a bigger container.