It's a slime 'mold '. Though it looks scary, this organism is not a mold nor fungus...nor does it cause any harm to the plant, the soil, nor you. Slime molds should be thought of as beneficial.

It will go away on its own soon enough.

Some more information about slime molds.

Here is a link that might be useful: About Slime Mold

in my plant dirt?

==>>> your choice of words.. make it almost sound like the plant is potted ...

to define a few words ...

'soil' is mother earth ...

pots are filled with 'media' ...

and 'dirt' is what is all over you .. after playing in either ...

if you have soil in a pot.. that might end up being a problem ...

more facts if you want more info..

what they said otherwise ..

ken