Planaxinae and Fossarinae showing important anatomical similarities, they have been grouped within a same family. But regarding the conchological features shared by these two groups, they simply do not exist.
 

Shell minute to small, turbiniform, often translucent. « The change from the larval shell into the teleoconch is drastic and occurs with a little more than three whorls completed. […] The fully grown shell consists of two or a little more postlarval whorls, which are sculptured by acute spiral ribs. Three of these ribs are more prominent, others between them are smaller. The number of ribs increases with the number of whorls. The base is covered by strong ribs and the umbilicus is partly covered by the thickened inner lip. » – Bandel & Kowalke: “Systematic value of the larval shell of fossil and modern Vanikoridae, Pickworthiidae and the genus Fossarus (Caenogastropoda, Mollusca)”, Berliner Geowissenschaftliche Abhandlungen Reihe A vol.190, Berlin 1997, p.5.
 

Shell small, smooth or with some spiral sculpture, littoriniform but with a wide anterior canal. The differences with the other genera of the Planaxinae are mainly anatomical.