Amerianna leopoldi is a relatively small species of freshwater snail in the family Planorbidae. It is named after King Leopold III of Belgium, but lives in the Arfak Mountains of Indonesia at high elevations. It has a uniquely shaped shell where the apex is concave, concealed by the body whorl.
Taxonomy Amerianna leopoldi was first discovered on March 9, 1929 in the Arfak Mountains in modern day Indonesia. It was subsequently described in 1931 by Paul Dupuis, though it was given the name Ameria leopoldi. Dupuis additionally described a larger variety of the animal, giving it the name Ameria leopoldi var. exersta. This variation is no longer accepted as being a valid classification. Phylogenetically, A. leopoldi is the sister taxa for a yet unnamed (as of 2026) species of Amerianna.
The name "leopoldi" is a tribute to King Leopold III of Belgium.
2 type specimens (cotypes) from Dupuis's original description are found in the collections of the Royal Belgian Institute of Natural Sciences.
Description The pale brown, translucent shell of Amerianna leopoldi is about long, though specimens as large as have been described. It is left-coiling (sinistral), with 3 shell revolutions (whorls). The top of the shell (apex) is concave, surrounded entirely by the body whorl. This characteristic shell shape is considered unique enough to identify the species. The outer layer of the shell, called the periostracum, may be hairy. The radula, a toothy tongue-like structure, is similar to other planorbid species, with one cusp on the middle column of teeth (lateral teeth).
Unlike other Amerianna species, the gill (pseudobranch) of A. leopoldi is not divided into a distinct front and back section. The ureter is S-shaped, distinguishing it from those of A. buruana and A. pesigani. Additionally, there have been no dorsal, renal, or rectal ridges observed in the mantle cavity, a space formed by the folding of the skin, which contains several organs. This further distinguishes it from A. buruana, A. pesigani, and A. obesula, which all have at least one ridge. A. leopoldi may additionally be distinguished by its triangular penis.
Distribution Amerianna leopoldi is known from the Arfak Mountains in West Papua, Indonesia, where it was discovered at an elevation of above sea level.
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