Turbonilla Risso, 1826 ex Leach

Høisaeter, Tore, 2014, The Pyramidellidae (Gastropoda, Heterobranchia) of Norway and adjacent waters. A taxonomic review, Fauna norvegica 34, pp. 7-78 : 61-63

Turbonilla Risso, 1826 ex Leach ms

Type species, by subsequent designation: Turbonilla costulata Risso, 1826 ; designated by Herrmannsen (1852). Mediterranean fossil.

Pyramidellids with elongate, slender, conical or cyrtoconoid, many-whorled shells. Sculpture consisting of strong axial ribs, without or with only microscopical spiral ornamentation. Shell white or semitransparent. Columellar fold only as a slight thickening on the inner lip. Protoconch of type A (helicoid, its axis at an angle of 90° to the main shell axis) or type B (planorboid, its axis at an angle of roughly 135° to the main shell axis).The protoconch is (usually) largely exposed, with the whole of its base visible and only part of the spire immersed in the teleoconch. Height of first teleoconch whorl, 200-280 µm. Operculum horncoloured, thin and translucent, with a small, excentric spire and without any ‘anchor’ or internal process.

Turbonilla was created by Leach in an ms written before 1818, but not published until 1846 (see Lovén 1846a). He intended the name to be used for a group of small shells superficially resembling Turritella . The name was validated by Risso who, in 1826, used the name for three fossil and one recent Italian pyramidellids: Turbo gracilis Brocchi, 1814 , Turbonilla plicatula Risso, 1826 , T. costulata Risso, 1826 , and T. humboldtii Risso, 1826 . According to Palmer (1958), the type species (by subsequent designation of Herrmannsen 1852), is the fossil, Turbonilla costulata . This species was regarded by most workers in the 19 th century (e.g. Monterosato 1884) as a synonym of Turbo elegantissima ( Montagu, 1803) , and the adoption of this species as genotype was certainly in the spirit of Leach. Dall & Bartsch (1904) apparently was unaware of this type designation, as they, without comments, lists T. plicatula (erroneously spelled T. plicata in their 1909-work) as type, but at the same time renaming the species T. typica , as they found T. plicatula preoccupied. Winckworth (1932) correctly cites T. costulata as type species, but most modern authors (e.g. Bartsch 1955, and Abbott 1974) uses one of the following names: T. typica , T. plicata , or T. plicatula . Bush (1899), Thiele (1929), and Nordsieck (1972) all use T. lactea as genotype, however.

Like many of the early genera in the Pyramidellidae , Turbonilla has been used both in a broad and in a narrow sense. In the broad sense it encompass all elongated species with a large, exposed protoconch and distinct axial sculpture (see e.g. G.O. Sars 1878, and Fischer 1887), a group that, especially in temperate and warm waters, exhibit a tremendous diversity. Dall & Bartsch (1904) adopted the name for an even broader group of shells, cylindro-conic, many-whorled, slender pyramidellids with a single columellar fold, with or without sculpture. The name was used in much the same sense by Kobelt (1903), though he was less categorical about the presence of a columellar fold. Thiele (1929), van Aartsen (1981) and Fretter et al. (1986) all use Turbonilla in the sense of G.O. Sars. In this review, the name is used in a narrower sense, only for pyramidellids with an elongated, many-whorled shell with axial sculpture (no spiral ornamentation), and an exposed protoconch.

Turbonilla sensu stricto is not a northern group. Only two species are treated here, one of those only because of some, probably erroneous, records from the 19 th century.

Key to the species of Turbonilla , based on shell morphology

1a. Protoconch planorboid with 135° to the shell axis ............................ Turbonilla lactea

1b. Protoconch helicoid with 90° to the shall axis ........................... Turbonilla pusilla