Everyone who ever put decent live rock into their tank has eunicid worms. Some of them are really small, while others grow to monster movie size. If you look closely enough, you'll see them. The largest I've ever kept was about the thickness of my little finger. He was vegetarian and I never did get to see how long he actually was....at least 12".
While commonly called bristle worms, eunicid worms are quite different. 5 distinct "antennae"...nasty mandibles...very fast moving...rarely seen completely out of a hole...and centipede like legs...usually shiny segmented body. They can be problematic..but they can just as easily exist in your tank for decades and you wouldn't know it.
Old picture...but still a classic.
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400 gal reef. Established April, 2007. 3 Sequence Dart, RM12-4 skimmer, 2 x OM4Ways, Yellow Tang, Maroon Clown (pair), Blonde Naso Tang, Vlamingi Tang, Foxface Rabbit, Unicorn Tang, 2 Pakistani Butterflies and a few coral gobies
My Tank:
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