please help with identifying

[houssic]

Got a bunch of these on the base of my hammer coral.

 

[ReeferKimberly]

little feather dusters and pineapple sponges, both good/harmless

 

[Crooked Reef]

Definitely pineapple sponges. Unless they grow so many that they start choking the hammer out, which is doubtful, they are beneficial. They do scrape off pretty easy though. If the hammer looks irritated by them just remove them. If not I would leave them.

 

[crvz]

I've generally found those type of sponges will stay out of direct light, so they should be of no issue. I've had them in large quantities in the overflows, if anything the likely aid in filtrated wastes from the water column (though doubtfully in a meaningful way).