A new species of the family Tritoniidae is described from the tropical South Atlantic Ocean. The animal was found off north-east Brazil. Tritonia khaleesi sp. nov. is up to 12 mm long, with a slender white body, of which the notum is covered with one broad white band extending from between the eyes and veil to the tail; veil with 4 velar appendages; retractable white rhinophores; rhinophoral sheath with fleshy extension; seven pairs of branchial plumes; the anus is located between the 3rd and 4th gills on the right side, and the genital opening is under the 2nd gill. Internally, T. khaleesi sp. nov. is distinguished from other tritoniids by jaws with 10–14 rows of denticles on the inner lips, absence of stomach plates and the radular formula 32 × 2–5.1.1.1.2–5 teeth. Tritonia khaleesi sp. nov. is the only Tritonia that possesses a unicuspid rachidian tooth as an adult.
