Don't take this as fact as I don't have the knowledge to tell you what to do but I would sterilize the tank... well, not really
I would not just dispose the ... whatever it is... I would transfer to another container with the gravel in the tank you want including the thing in question. I am a little bit of a 'tree huger' so would never just dispose of something just due to my lack of understanding. Sigh, I'd probably start another small tank for the beta and leave what you see alone to see what happens. I just could not dispose of something that appears to be alive just because I lacked the knowledge to know what I was dealing with. It would be easy to just say to kill the tank, boil the gravel, just totally kill the tank and start over but I could not do that myself without knowing what I was killing.
Keep in mind that I'm speaking in total ignorance but I would never just dispose of something just due to a lack of understanding.
I NEVER forget... I just remember late.