What is this?

[Domboski]

The last two are videos and may be more telling. These are all over the glass. I assumed they were some kind of hydroid but now I'm not so sure. I just got a Oxymonacanthus longirostris back from a customer and it immediately started eating them.

 

[Domboski]

Thanks to skatezen for confirming it is Staurocladia. So cool how much life there is in the marine world. I had no clue there was "walking" hydroids

 

[KathyC]

There sure are, it is Staurocladia oahuensis to be specific
These are not the colonial type hydroids that become such a pain, then tend to go away on their own after a time and don't increase to plaque type numbers either.