Taxonomic revision of Pisulina (Gastropoda: Neritopsina) from submarine caves in the tropical Indo-Pacific.

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Species of the tropical Indo-Pacific gastropod Pisulina (superorder Neritopsina), previously known only from empty shells and regarded as a genus of Smaragdiinae (Neritidae), are revised on conchological criteria. Pisulina dwells in gloomy to totally dark, tropical and subtropical, shallow-water submarine caves, where their empty shells are ubiquitous. Study of the previously described modern and fossil species and examination of newly collected material from more than 50 submarine caves on Pacific islands show that there are six species in the genus : P. adamsiana Nevill and Nevill, 1869 (Holocene), P. subpacifica Ladd, 1966 (late Miocene), P. biplicata Thiele, 1925 (Recent), P. maxima new species (Recent), P. tenuis new species (Recent), and Pisulina sp. (Pleistocene). An analysis of previously unstudied shell characters (shell form, shell microstructure, protoconch morphology, and opercular features) of Pisulina and other modern, representative genera of Neritopsina places the genus close to the freshwater and brackish-water genus Neritilia, based on three unique characters (inclined protoconch, spiral ridges on the protoconch surface, and perpendicularly arranged prisms in the outer shell layer), and both genera are herein included in the family Neritiliidae. This study shows that the protoconch and shell microstructure analysis is important for re-evaluating fossil species previously placed in Neritidae.
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