Its bladderwort.
Thrives in low light low nutrient environments carnivorous plant. The little bulbs on it are traps for small critters like cyclops and such but can be bad news with baby shrimp and baby fish.
Even a small thread hitchhiker on another plant will grow into this mass clump very fast.
Ive thrown mine into my goldfish tank lol
Here's a view of mine under a weak microscope
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And my clump kept in a breeder net in the goldfish tank, taking over my hornwort and duckweed and everything else lol
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You can put it in a jar in a sunny window and let it be, it'll grow. Harmless mostly, unless you've got fry and shrimplets. It can be a messy tangle plant that can choke out other plants too. It floats.