OK i just realized that I called the "slug" and arthropod. Sheesh, I feel embarassed to be a biologist. Shame on me. If it is indeed a slug, it would then be a gastropod and therfore grouped in with the mollusks. Anyway you say it though I certainly have never come face to face with one of these!
I don't have a photograph, but a couple weeks ago I found something had made a mess of the soil in the pot with my Bletillas outside. So, I packed the soil back in and a toad jumped out and scared the crap out of me! I didn't scream but I definitely dropped the pot. I guess he liked the cool, damp soil and felt like taking a nap.
More stories of orchid pot "companions!"