i beleive they are spagethi (sp) worms, they are a common reef hitchhiker that willhelp to keep your tank clean of any detrius. May i ask how long the tank has been set-up and what type of "starter fish" you have, most lfs will sell you damsels or something like that to "Cycle" your tank, this is not needed as the live rock and sand will cycle itself, all you have to do is add a tiny bit of fish food to keep the beneficial bacteria growing, most of the time people find out way to late that the starter ffish they have they no longer want when it comes to actually stocking the reef, it is better to just wait for the cycle to end, then add fish slowly, starting with the hardiest fish first, then going into the more delicate fish as your tank matures. just a thought though
