This group of molluscs has similar animals, radula and shell morphology. There are a small number of species within the group, many of which have highly unusual shell characteristics. Shells of this group are lenticular in shape; spires are about as long as apertures; sculptured with punctate spiral grooves; lower body whorl is often smooth. This sculpture facilitates movement into and out of white coral sand. Animals of this group are generally milky-white in color with a white siphon and foot. Eye stalks are often brown, the eye being hidden within a dark-brown color band.
This group of shells appeared first in fossil records during the Holocene (recent fossils), indicating a rather recent adaptation to new habitats.
The radulae of the species within this group are simple, with small sickle-shaped lateral rachidian with 3 to 5 enlarged cusps. The central rachid-ian is fan-shaped often with matching pairs of needle-like cusps. Cusp count varies from 6 to 8 on the central rachidian.
Swainsonia was been treated by Cernohorsky 1970 & 1991 as a subgenus of Scabricola based on the similarity of radula, shell shape and habitat. Kaicher 1974 elevated the genus of the type species Swainsonia fissurata to full generic level without stating a reason. Based on observations of the animal of Scabricola variegata, type species of the genus Scabricola, which has an animal similar to that of Nebularia species, we concur with Kaicher and treat Swainsonia as a full genus. The genus Swainsonia animals are similar to the Mitra group of species while the genus Scabricola animals are similar to the Nebularia group. There appears to be a parallel development of similar features (radula and habitat) between these two groups of shells.