Anatomy and Systematics of the Submarine-Cave Gastropod Pisulina (Neritopsina: Neritiliidae)

The soft parts and radula of Pisulina adamsiana and Pisulina maxima (Gastropoda: Neritopsina) are described for the first time on the basis of specimens collected alive from nine submarine caves of tropical to subtropical Pacific islands. To clarify the systematic position of Pisulina within the Neritopsina the fresh- and brackish-water genus Neritilia is also examined anatomically. The close relationship between Pisulina and Neritilia is confirmed by 19 unique, unreversed, possible synapomorphies: (1) an inclined protoconch; (2) spiral ridges on the larval shell; (3) almost perpendicularly arranged prisms of the outer shell layer; (4) open-pit eyes; (5) female flap on the foot with a ciliated neck furrow from the mantle cavity; (6) caeca on the visceral mass and corresponding shell pores; (7) reduced left ctenidium; (8) right hypobranchial gland composed of single-type cells; (9) two complicated pairs of oesophageal glands; (10) another pair of ovoid glands in the oesophageal floor; (11) inner lateral tooth of radula with a largely expanded lobe; (12) elongated outer lateral tooth with an oblique, comb-like blade; (13) a lateromarginal plate; (14) single large aperture of the digestive gland into the stomach; (15) strongly curved rectum on the pallial roof; (16) transverse slit-shaped vaginal opening situated far back from the female opening and anus; (17) absence of independent duct from the seminal receptacle to the albumen gland; (18) very long, club-shaped spermatophore sac extending to the pericardium; and (19) doubled seminal vesicle. Pisulina and Neritilia constitute an independent family Neritiliidae, together with the Miocene genus Pisulinella. The discovery of the open-pit eye in Pisulina and Neritilia, hitherto unknown in Orthogastropoda, suggests that the genera evolved from an ancestral species that lived in dark submarine caves.