Katsuyu

Katsuyu is the slug queen summon of Tsunade. Compared to Gamabunta and Manda, the summons of Jiraiya and Orochimaru, respectively, Katsuyu is quiet and more subservient to her master. With her Slug Great Division, Katsuyu can divide herself into smaller slugs to evade attacks or to serve small scale functions, and is able quickly reform herself if need be. She can also spit acid for her Tongue Tooth Sticky Acid, which is strong enough to melt through rock.

(Source: Naruto Wikia)