Is this a pest????

[russ13]

I was at a local reef store and found a nice SPS I wanted to pick up. Then in the same tank I saw this guy on another SPS. After doing a bit of looking I saw three more crawling on other sps corals. Not the best pic they're little slugs with long antenna one had bubbles all over it???

 

[russ13]

 

[Mikeatt86]

Looks like a lettuce slug what color was it

 

[coral102]

Where is it at???