I just had 'em....came in on a channel cat from a LFS I'm possibly never going back to. Get some parasite clear tablets (Praziquantel, Diflubenzeron,, Metronidazole, Acriflavin) and treat 'em like fish lice or anchor worms....treat for 3 weeks w/ 25% WC each week. As always remove carbon elements and boil before returning to the tank after treatment.
Not 100% sure what they were but that stuff did away with them. Might cost a little; $5 per 8 tablets, but it's good stuff. Dissolve the tablets in a bucket of water 1st since your tank is over 40G. U do all that and you'll be good in no time. Catty was still doubling his weight while the treatment was going on. I used full dose and didn't consider skin vs. scales for medicine, and he didn't even care. He went from 3" to almost 6" in a month since I bought him.
Hardier species of scaleless fish. Found this out years ago by accident.
twhittle