What is this??

[Chaz303]

Hello! I’m very new to the marine tank life! I recently purchased a hermit crab (last week) and I’ve noticed that there is a hitch hiker on his shell! Any ideas what it is? Its head is the shape of a slug, but it’s what it seems to be living in that is throwing me! Sorry I didn’t get a picture of its head, it’s very fast, but it seems to be feeding off the algae when it gets a chance.

 

[kfisc]

Looks like a barnacle of some sort. Harmless filter feeder if it is. Welcome to the site, tons of great information here.

 

[Reefing102]

Agreed, looks like a barnacle

 

[seymour47]

Definitely a barnacle. You've got a mobile surface cleaner with the hermit and a ride along filter feeder. Great combination. Plus, barnacles are just fun to watch wave their little fans around.