Another chaeto hitchhiker: Worm?

[SuncrestReef]

My chaeto has dozens of these small white critters. Here are some macro shots to see the detail, but the actual specimens are only about 1-2 mm in length. As you can see they are about the same width as a filament of chaeto, so less than 1 mm thick. These photos are of the same specimen from different angles. Are they some sort of worms?

 

[Lovemyreef2015]

Looks like the casing to a vermetid worm.