Retusoida

Retusoida is a genus of small, freshwater snails with a gill and an operculum, an external shell closure. The genus is endemic to New Zealand and includes two recognized species: Retusoida retusa and Retusoida truncata. These snails are characterized by their small, conical shells with a smooth, rounded apex and a slightly flattened base. The shell is typically brown or reddish-brown in color, with a glossy surface.

Retusoida snails are found in various freshwater habitats, including streams, rivers, and ponds. They are herbivorous, feeding on algae and other plant material. The genus is of particular interest to scientists due to its unique evolutionary history. Retusoida is one of the few freshwater snail genera that has evolved independently in New Zealand, separate from the main radiation of freshwater snails that occurred in the Northern Hemisphere.

The taxonomy of Retusoida is still a subject of ongoing research. Some authors have suggested that the genus may be more closely related to other freshwater snail genera than previously thought. However, further genetic and morphological studies are needed to fully understand the evolutionary relationships within this genus.

Retusoida snails are not considered to be of significant economic importance, but they play an important role in their ecosystems. They contribute to nutrient cycling and help maintain the health of freshwater habitats. Despite their small size, Retusoida snails are fascinating subjects for study, offering insights into the diversity and evolution of freshwater mollusks.