I got up this morning and as I was turning the lights on in my 2.5 gallon aquarium some movement near the surface caught my eye. It was this tiny little dome shaped creature jetting around the tank, fighting the current. Like I said, it's small, bullet shaped, seemingly hollow, has two tiny little algae green tentacles, and is always swimming toward the light. I'll try and put a picture up if I can get one. It's so small the camera is having trouble focusing on it. Any ideas as to what is is? Thanks.