Acid Slugs

Acid Slugs are gargantuan mollusks whose bodies secrete a corrosive mucus capable of causing mild chemical burns. They appear in Ultima VI, Ultima VII, Ultima VII Part Two, and in the Ultima Underworld series.

Description
Generally found in dark, wet environments such as dungeons, caverns, and swamps, acid slugs have an acute sense of curiosity and will frequently approach travelers to investigate them. Due to the toxic nature of their bodily secretions, however, encounters with these beasts often prove problematic, especially given that their bodies have a tendency to wear on conventional metal weaponry. A canny adventurer, however, will find that these creatures are extremely susceptible to fire and will be able to quickly dispatch them with the aid of a common torch.

Trivia

 * Acid slugs have been portrayed differently throughout the series. First appearing as pale pinkish blobs in Ultima VI, these beast later came to be shown as white, blue veined creatures in Ultima VII, whereas in the Ultima Underworld games, they were consistently portrayed as green.