Quarantine the CUC?

In my opinion if it is wet it gets QT.
The reason is that when parasites like ich falls off, it attaches to a hard substrate. This is often snail & crab shells, so if you dont QT, you may be introducing ich into your tank with never having a fish.

 

An welcome to the site!

 

I've had shop owners say, its a clam, you don't need to quarantine. Its bull ****. Xroads did some comprehensive presentation on parasites and desease. Ich has a cist cycle that can last 3 weeks. This cist latches on anything in the tank (clam shell).
I'm on my third setup and I've been a QT Nazi. No problems at all. Powder brown tang is 3 months ich free, tons of livestock added.
Also, stuff can hide in the crevices of frags. Is a good practice to pick up a bottle of iodine in the first aid section of your favorite drug store. After QT a climate to your DT and when your pH & salinity is close add iodine to a tea color. Pretty dark. Give them 5 minutes. Draw a container water out of your DT. Shake corals out in this water and then place in your DT. This kills any invertebrates that may be hitchicking. Some worms eat acropora along with other inverts. This ensures they don't get in and give you headachs.
More advice. If you added something to your QT and started your 3 week cycle. Avoid getting the urge to add anything or you should start the time over.
Pay attention to the needs of fish you quarantine. I had a blue spot jawfish go belly up. I suspect he was over stresses because there wasn't a sand bed to hide in.

 

Just to clarify. Ich does not infect the snail. The life cycle has a cyst stage that latches on anything in the tank. Each cyst releases a plethora of free floating paracites. These free floaters are what attach to the fish, feed, drop off, cyst again and then continue the cycle. If you remove the fish the ich cycle stops.
Happy reefing. Google ich cycle for more reading.