Slug

are the trademark summon of Tsunade, also known as.

Overview
Slugs' offensive abilities seem to revolve around shooting acid from their mouths, similar to the way toads use oil. Slugs have also been shown to be able to divide themselves into many smaller replicas, though this ability may be unique to Katsuyu due to her size. For defending others the slugs have the ability to encapsulate themselves around an individual's entire body. This essentially makes them a big cushion for the person inside, protecting the person from physical collisions. Slugs can also absorb chakra from their summoner and even control it to some extent, as shown when Tsunade transferred her own chakra to Katsuyu in order to heal the citizens of Konoha when Pain attacked.

Known Slug Abilities

 * Tongue Tooth Sticky Acid
 * Chakra Transfer Technique
 * Slug Great Division

Known Slugs
The personal summon of Tsunade. With its great size and abilities, it fought side by side with the others two great summonings of the sannin, Manda and Gamabunta.
 * Katsuyu
 * Saiken

Trivia

 * The acid-shooting powers are an exaggeration of real-life slugs' ability to regurgitate digestive acids in self-defence.
 * Katsuyu has been the only slug seen summoned by Tsunade in the series to date. The other slug seen in the series is the Six-Tails. Kishimoto has however drawn three other slugs: one on the the cover of chapter 4, another on the cover of chapter 153 and the third in the colour spread of chapter 162.