Here's a pic of Spirorbid worms:
Some info. on them here (they are harmless, and common in new tank setups): Reefkeeper's Guide to Invertebrate Zoology: Part 10: Sedentary Polychaetes, Con't.
See the section on Spirorbidae
Here's a pic of the Hydroid Jellies:
More info. here: "Dots with Legs" - Odd Critters, Dr. Ron Shimek
Coraline would tend to have a pink-ish color, and look more like a splotch on the glass (it always reminds me of fading/peeling paint spots).
In any case, none of the above three are harmful.
Maybe someoneone else has some other ideas? Any snails in the tank? Could be some sort of snail egg??