im new to fish keeping but i fort that my harlequins were pregnaut due to putting alot of weight on there are a few bits of what looks like frog spawn stuck to the glass in a few areas. so not sure if the snals have left this of the fish
Most likely they are snail eggs. Harlequins have a complicated reproductive dance that they do when they lay their eggs and they usually like to lay them under a leaf or something similar to that. Snails will just lay their eggs anywhere and they will reproduce and take over a tank very very quickly.