Eatoniella mortoni is a species of marine gastropod mollusc in the family Eatoniellidae. First described by Winston Ponder in 1965, it is endemic to the waters of New Zealand. The species has been used to study the effects of ocean acidification, as it is known to thrive in carbon dioxide-rich environments.
In the original description, Ponder described the species as follows:
E. mortoni measures by . It can be identified due to its moderately large, D-shaped aperture, ovate-conical, smooth shell with a spire slightly taller than aperture, and by its colour, which varies between purple-tinted dark grey to pale yellowish-grey.
The species was first described by Winston Ponder in 1965, who named it Eatoniella (Dardanula) mortoni. Ponder named the species after New Zealand biologist John Morton, who had assisted Ponder during his early investigations into the species. Ponder synonymised several previously-named genera, including Iredale's 1915 genus Dardanula, which was retained as a subgenus of Eatoniella. The modern formatting of the name without a subgenus, Eatoniella mortoni, was established by Hamish Spencer and Richard C. Willan in 1995. The holotype of the species was collected by Ponder himself on 11 December 1961, from the south side of Days Bay in Lower Hutt. It is held by the Auckland War Memorial Museum.
The species is endemic to New Zealand, known to occur on both coasts of the North Island and South Island. In addition, the species can be found on the Chatham Islands and the volcanic island Whakaari / White Island.
Typically the species can be found on algae at low tide, underneath intertidal rocks, and often lives on kelp species such as Ecklonia radiata.
Eatoniella mortoni has been used as a species to study ocean acidification, as the species benefits from living in carbon dioxide-rich environments and remains localised, especially specimens sourced from the volcanic island Whakaari / White Island, due to their lifetime exposure to carbon dioxide vents. Eatoniella mortoni can produce more crystalline, durable and less porous shells at natural carbon dioxide vents.