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Key to Extant Species of Vorticifex
Living species of Vorticifex (sometimes placed in the separate genus or subgenus Parapholyx) are mostly poorly studied, aside from some of those dealt with in Baker (1945). Their relationships to the numerous Late Cenozoic forms also need to be clarified. Anatomical discriminants in this group appear to be comparatively subtle. We have retained the current classification, mostly derived from Baker (1945), as the subspecific epithets are likely to be valid; however, certain of the subspecies are likely either to be recognized eventually as full species or to show closer relationships to taxa currently assigned to another species or undescribed.
This genus is strongly atypical for a planorbid, being a stream-adapted, cold stenothermal taxon most typical of cold oligotrophic flowing-water habitats of medium-large size. In some ways, its ecology is much closer to that of the aberrant limpet-shaped lymnaeid group Lancidae (with which they often occur) than to stereotypical Planorbidae.
| 1 | Shell neritiform, thick; aperture thickened around whole periphery, so that opening evidently constricted Shell thin; neritiform or with low spire; callus at columella and base only |
neritoides
2 |
| 2 | Shell neritiform Shell with short spire or almost neritiform |
3 4 |
| 3 | Shell large, to 2.5 cm diameter; very thin, cinnamon-colored; no varices or periostracal fringes Shell large, to 2.5 cm diameter; very thin, yellowish, with prominent regular periostracal fringes and underlying shallow varices |
klamathensis klamathensis effusus dalli |
| 4 | Shell with definite spire Shell with very low spire or nearly neritiform |
5 6 |
| 5 | Shell solid but not thick; to 2 cm diameter; juvenile whorls rounded; no varices Shell comparatively thin; less than 1 cm diameter; juvenile whorls strongly keeled; prominent varices, with or without small periostracal fringes |
klamathensis sinitsini n. sp. 1 |
| 6 | Shell thin to somewhat solid; diameter to 3 cm; with several low diagonal ribs on final whorl Shell typically somewhat solid; diameter generally 1 cm or less; surface nearly smooth, with very fine growth lines; occasional scattered low periostracal fringes; no varices |
effusus diagonalis effusus effusus |
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