The Legendary sannin Jiraiya, Orochimaru, and Tsunade have summoning contracts with toads, snakes and slugs respectively. While Jiraiya and Orochimaru summon different toads and snakes on different occasions, Katsuyu is the only slug that Tsunade has summoned.
Later, their students, Naruto, Sasuke, and Sakura gain their summoning techniques. Naruto and Sasuke summon different toads and snakes. However, when Sakura summons a slug in Chapter 634, it is Katsuyu again.
Are there any slugs besides Katsuyu in the Naruto universe?