it's possible they are baby snails since snails feed on algae. now as to what kind, i am not sure until they grow bigger. try brushing them off with a new unused "tool" (spatula or chopstick, etc) and see if they move, if they latch on or move on the moss to another place, they are some kind of living things. make sure you have never washed the "tool" with detergent, just wash it with hot water.
Or you can pick up the moss ball and dip it in tap water with a dash of table salt for a few (5 or less) minutes and see if they detach. Then you get most of them out this way. oh rinse in tap water thoroughly using your fingers to brush against the moss (wear gloves) but do not squeeze the moss ball after that.
Last edited by Otterfun; 02-08-2013 at 12:16 PM.