Most LR holes are caused by dissolution, rock-boring sponges, rock-boring clams, and rock-boring urchins. There are a few algaes that can bore through rock and so can spionid worms (mud worms, oyster-boring worms).
While I suspect that these are just regular bristleworms eating a dead cold-water clam that cannot tolerate reef tank temperatures, it is possible that you did import parasitic worms with the clam.
Spionids are parasitic to various oyster, mussels, abalone, clams, scallops, etc. Basically, most bivalves. If you think that these holes in your LR are new then maybe they killed off your cleaner clam and they are looking for a food source. If you have a decorative clam in this tank, I would quarantine it and inspect it's shell (particularly near the foot and byssal threads) for small holes and worms. By any chance, do you know the species of cleaner clam? The only cleaner clam I could find on google was at Saltwaterfish.com and they didn't give any info whatsoever. I also found this thread on 3 reef.
Benefits of Clam