Sea snail or slug?

[huckjai]

Noticed this tiny thing clinging on my glass. Moves like a snail. Had two antennae. Any idea what it is? Good or bad? Thanks.

 

[huckjai]

Decided to remove it in case it's a bad one. It's some sort of snail.

 

[DSC reef]

Collonista snail, good guy

 

[Mikedawg]

Collonista Snail | Melev's Reef

The subject of this picture is the tiny snail in the dead center. It is a Collonista amakusaensis, which is quite a mouthful for such a tiny guy. It is about the size of a BB, and is hiding in the shade of an Astrea above. These tend to come in as hitchhikers, and breed quite easily. If you look...

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