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Most of the 1,542 species in the molluscan Class Gastropoda (snails and slugs) that have been recorded from the Marshall Islands are marine prosobranch ("gill-breathing") species. There are, however, a small number of pulmonates (or "lung-breathers"), as well as just a few prosobranchs, that live on land or the intertidal zone, or in freshwater or in brackish areas, such as "iaraj" pits. Although pulmonates have a lung for breathing air, some species do remain near the ocean and may be underwater, at least part of the time. Others that are part of the land ecology.
Pulmonates and other non-marine snails deserve special attention because, throughout the world, they include some of the most threatened - and threatening - of all snails. Because of the small size of most of these species, some of them almost certainly were inadvertently introduced to the Marshalls aboard the canoes of old and the ships of more modern times. Other large species have been intentionally introduced with the idea of providing food, medicine - and even pets - for people.
All three of these reasons are how the giant African snail (Achatina fulica) has spread throughout the tropics. Although still kept by some persons as a pet, this species is recognized as an agricultural pest. With its large size and voracious vegetarian appetite, it can easily chomp plants down to their roots, destroying valuable food and agricultural crops. This species is not common in the Marshalls but has been found here.
In some areas of the Pacific, another exotic snail, a Floridian native, Euglandina rosea, was introduced for the purpose of being a biological control of the giant African snail. Sadly, not only did this introduction not solve the problem, but it proved the old adage that "two wrongs do not make a right."
E. rosea, it turns out, prefers to prey on native snails, swallowing them down whole, rather than on the giant African snail. On other islands of the Pacific, such as Moorea, Hawaii and American Samoa, this species has decimated the formerly glorious native land snail population, causing the extinction of some endemic species and driving many other endemics to the brink of extinction.
Fortunately, E. rosea has not been reported here - so far! But if it is introduced, it could easily adversely affect the biodiversity. The Marshall Islands has its own assortment of native land snails, even some rather attractive species, and one endemic subspecies. One pulmonate and one prosobranch have both already been considered to be of conservation consideration by the IUCN.
Native pulmonates and other non-marine snails of the Marshall Islands are not simply scientific curiosities. The three seaside species of "alu" (Melampus spp.) are, for example, valuable biological resources, popularly being used by women in their handicrafts, in making decorative hairclips, pins and shell vases and to adorn baskets.