Evolution and systematics

The earliest unequivocal record of the order Neritopsina is Late Sularian-Devonian (428-374 million years ago). Earlier Ordovician records are based on protoconch and adult shell similarities. The Neritopsina were noted as being very distinct from other "archaeogastropods" in the early twentieth century, but only since the 1970s has that placement been broadly accepted.

Neritopsina coil their shells differently than other coiled gastropods and therefore lack a central shell axis, the columella, and most species absorb the internal partitions of the shell as they grow, permitting the snail's body to be more limpet-like rather than coiled, irrespective of its shell.

The Neritopsina are the first clade in the gastropod lineage that has undergone the extensive evolutionary radiations observed across the Gastropoda. The group has shell morphologies that range from coiled conical snails (Hydrocenidae) to limpets (Phenacolepadidae), and even slugs (Titiscaniidae). While conical shells are seen in Hydrocenidae, none appear to have developed very high-spired shells. Multiple terrestrial (Helicinidae, Hydrocenidae) and freshwater invasions have oc curred (Neritidae), with some freshwater taxa still having an estuarine or marine larval phase.

The order Neritopsina contains the families Neritidae, Phenacolepadidae, Neritopsidae, Helicinidae, Hydrocenidae, and Titiscaniidae.

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