Completing an unattended to apple cider vinegar
If you are making your own cider vinegar, you might want to be come familiar with what you are likely to see by doing some research first.

I have to assume that you are referring to the "mother" which is a standard, normal part of the vinegar fermentation process. Say hello to acetobacter, they are doing the work you require. Even if they do look a bit slimy and disturbing en masse.