An Undine (ウンディーネ, Undīne) is a female water guide who take sightseers around Neo-Venezia on their gondolas. The job originated from Manhome and was introduced to Aqua. There are many Undine companies, and the top two are Orange Planet and Himeya. There are three ranks of Undine: Pair, Single and Prima.
An Undine who has just begun practicing sculling a gondola. A Pair is recognized by her pair of gloves, worn to protect her hands as she builds up calluses. When a Pair is promoted to Single, she removes one glove. This is translated by Nozomi and ADV as "Pair" and by Tokyopop as "apprentice".
An Undine who is qualified to take customers only under supervision. So called because she wears only one glove. This is translated by Nozomi and ADV as "Single" and by Tokyopop as "journeyman".
An Undine who is no longer a Single. Once an Undine becomes a Prima, they can take customers without supervision. This is translated by Nozomi and ADV as "Prima" and by Tokyopop as "graduated Undine".