Should I remove this larvae(?) friend or foe?
Very new tank, 36litres (around 10gallons), been set up 4 days, and both invited (Ramshorn snails) and uninvited (a bladder snail and various teeny tiny critters) are settling in. But this little friend(?) popped up today and I'm not sure if he's going to cause trouble!
He's about 2cm/1inch long when he's fully stretched out, very dark black spot one end, and a little round ... Maw? The other end, it's got grabby bits (3rd photo). With a rounded transparent body. Moves in waves like a worm, nudging the sand out the way.
He's popping up from the sand periodically, black end up, and then burrowing back under, but never sitting on top or swimming. Possibly he's not actually aquatic and isn't enjoying the water. Possibly he will become a monster and eat my brain while I sleep. Possibly I should just leave him be.
Help?