Looks like Planaria to me. You have gravel in your tank, a big problem with gravel is that you can never get ALL of the fish waste/fish food even with thorough gravel vacuuming. This is why I'm a strong supporter of bare bottom tanks. Also, it looks like you have more than an inch and a half thick of gravel. I recommend you remove some of the gravel(or all of it) and do a huge vacuuming.
Someone stated that they(Planaria/worms) will eat your eggs and that you should nuke them with meds. Not true. Do not give out false info if you don't know what you're talking about. Just do big gravel vacs and you should be fine. I recommend you go bare bottom. HTH's