Shells minute, rounded, depressed to globose, thin-walled, somewhat translucent. At this time, there is only one genus in the family.
 

Protoconch smooth or with some minute micropits. Teleoconch with numerous spiral rows of micropits. Umbilicus wide. Presence of radula. The genus is named after Tjärnö island and marine laboratory, Västra Götaland, SW. Sweden.