The Stallions of Ozajiarh
The rock pythons also are able to adhere to any stone surface by means of a long track of adhesive slime, a gastropod-like organ that is essentially the animal's entire underbelly, which it expands and contracts as it crawls along walls and ceilings.
Cursed!
He shut his eyes again to try and ignore the horror; to make it go away, but he could feel his guts churning as the last of his bones were broken down and his internal organs became those of a slug, a gastropod mollusk with no bones of any kind except a kind
[DolphinSanity] Yes, Commodore (Chapter 3)
The creature's four-inch length, minimal variation in girth, and movement patterns all could've helped it be mistaken for a worm at a distance, but the shape of it was definitely more like a gastropod in its details.
The Cage
Flesh of his dual cocks as they swelled to accommodate the slugs that were crawling into his tight, warm, moist urethras...other slugs crept along the exterior of his shafts, smothering them with mucus and slime before joining the procession of fat and slimy gastropods