snail spawn

Anyone know what part of a snail tho could be? my nassarius was climbed up on a rock and I could see an extra tube like part that was not the nose… https://youtube.com/shorts/9F5JZiSNdLE?feature=share

So about 3 weeks ago I added a very large single snail to my tank. I believed it was a Trochus snail. But it was sold as an omen snail according to my LFS. When I first got him he has been fine but has just been on the glass and not touched my rocks or substrate. It is very large around a £5...