I wrote the following about the toothed sucker rings of the Humboldt squid in Squid Says: What's For Dinner? Probably Not You:
Each ring would barely fit on the finger of an infant, and the "teeth" range from the length of a pinhead to microscopic. An armful of these sucker rings raking across your skin is like being scratched by a lot of very small cats. Ouch, but far from deadly. If you were a fish, the sucker teeth wouldn't even get under your scales. Their purpose, like the "toothed" tongue, is similar to Velcro, and consequently the arms and tentacles are very, very good at holding onto things.
In that essay, I didn't go into any more detail. But I do have some pictures of just how "ouch" the injuries from these sucker rings can get:

It must be noted that neither the injuries pictured here, nor any others I've received from squid, have ever scarred. Unlike the wounds my cats have inflicted on me . . .