I've seen theee white little critters suddenly pop up in the return chamber of my HOB skimmer and there's even some in the return cup inside the tank. I've even seen a few of them in the crevices of my live rock. Are they good, bad, if anyone knows, a reply would be very much appreciated.
Yeah, pineapple sponges. Harmless filter-feeders. They tend to surge and then fade out a bit, but established tanks often have tons. You can scrape them out of anywhere they're causing any actual problems, but I would leave them alone wherever they aren't in anything troublesome.