Shells minute, « discoidal, spirally involute; aperture entire, orbicular; operculum horny, circular. » – G. O. Sars: Bidrag til Kundskaben om Norges arktiske Fauna. I. Mollusca Regionis Arcticae Norvegiae, Christiania 1878, p.215.
 

Shell « discoidal, flat, paucispiral; whorls slightly angulated; aperture entire, almost completely round… » – A. Vayssière: “Observations zoologiques et anatomiques sur l’Ammonicera, nouveau genre de Gastéropode Prosobranche”, Annales de la Faculté des Sciences de Marseille vol.3, Marseille 1893, p.19.
 

Shell « nautiliform; spiral flattened; aperture lateral, peristome almost adjoining; operculum paucispiral, nucleus central. » – G. O. Sars: Bidrag til Kundskaben om Norges arktiske Fauna. I. Mollusca Regionis Arcticae Norvegiae, Christiania 1878, p.215.
 

The genus is monotypic. « The shell of Retrotortina consists of one protoconch whorl and 1.25 to 1.5 teleoconch whorls. […] The protoconch has one whorl, 175 to 200 µm in diameter, quite smooth with an inconspicuous ridge along its short adapical suture […]. The shell surface of the teleoconch has conspicuous growth lines[…]. The aperture is rounded except for a straight columellar edge […]. The operculum is paucispiral, coiling counterclockwise as seen from its outer surface, with flexible edges, and fits exactly the aperture when the animal is retracted. […] Retrotortina is diagnosed by very contrasted flat adapical and umbilicate abapical sides. » – Gofas & Warén: “Europe’s smallest gastropod: habitat, distribution and relationships of Retrotortina fuscata (Omalogyridae)”, Cahiers de Biologie Marine vol.39, Roscoff 1998, p.10.