What are these?

[Jrco226]

Came back home from a weeks long vacation and saw these along the glass and rock work. Last picture is neck to a snail for size comparisons. Are they good or bad?

 

[Elementalj]

Looks kinda like this.

http://www.lionfishlair.com/hitchhiker/dorvilleidae.shtml

 

[Lionfish Lair]

Yup, that's what they are. I adore them.

 

[Jrco226]

Okay, so not bad at all? There is a bunch of them. Crazy the population exploded that much after being gone 7 days. Thanks for the replies!

 

[Elementalj]

I've never seen them do anything other than crawl on the glass. [emoji1611]