Littoraria irrorata, also known by the common name the marsh periwinkle, is a species of sea snail, a marine gastropod mollusk in the family Littorinidae.

This is displayed in its strong relationship with Sporobolus alterniflorus, also known as Spartina alterniflora, a grass commonly found in abundance in salt marshes.

The snail has the ability to retract its foot into its shell when experiencing thermal stress which allows them to avoid water loss by evaporation and survive in high temperatures.

L. irrorata also deposits faeces on the wounds that they create, which encourage the growth of the fungi because they are rich in nitrogen and fungal hyphae.

Juvenile snails raised on uninfected leaves do not grow and are more likely to die, indicating the importance of the fungi in the diet of L.

[9] L. irrorata is capable of having a strong top-down control of S. alterniflorus production due to its grazing of the live shoots.

[15] In order to avoid predation, L. irrorata has the ability increase the thickness of their shell ridge which in turn decreases the size of their aperture opening.

This is an essential function to have as blue crabs are commonly seen chipping away at the shell ridge in order to feed on the snail.

[16] The Deepwater Horizon oil spill had major impacts on the productivity, population density, and growth of L. irrorata in salt marshes along the Gulf of Mexico and southeastern United States.