Odostomia Fleming, 1813

Type species, by subsequent designation: Turbo plicatus Montagu, 1803; designated by J.E. Gray (1847:159); Salcombe Bay, Britain.

Pyramidellids with, usually, small (<5.5 mm long), broadly conical or ovate shells, of not more than seven whorls. Sculpture, if any, confined to microscopic spiral striae or fine lines of growth. Shell white, sometimes with a grayish, yellowish or bluish tinge. Aperture rhomboid to oval, usually acute-angled above. Columella usually gently curved, merging almost imperceptibly with the base of the penultimate whorl. A columellar fold always present. Protoconch partly submerged in the teleoconch, its angle of inclination varying, though usually around 90° (type A, and B). Operculum with an opaque, opercular ‘anchor’ of varying thickness and with or without a distinct indentation and groove created by the columellar tooth.

In northern Europe, this is the dominating group of pyramidellids, both in number of species and number of specimens. Many of the forms here included are extremely common in their particular habitats in shallow water. I have included nine species from the treated region in this genus, but do not exclude the possibility of reducing the number further when more is known about all of the species.

Key to the species of Odostomia, based on shell morphology

1a. Protoconch around 120° ................... Odostomia striolata

1b. Protoconch 90° (type A) ..................................................2

2a. Protoconch partly submerged, sometimes with series of list-like teeth inside of outer lip, with a narrow spiral incision around periphery ........................‘ Odostomia’ conoidea

2b. Protoconch completely exposed ......................................3

3a. Shell tall (to 9 mm), pointed, often pinkish or brown, often with series of list-like teeth inside of outer lip, clearly prosocline growth lines ........................ Odostomia conspicua

3b. Shell not exceeding 5 mm, white, not with series of list-like teeth inside of outer lip .......................................4

4a. Whorls well rounded, orthocline growth lines, distinct umbilicus ................................ Odostomia acuta

4b. Whorls convex, suture deep, prosocline growth lines ...................... Odostomia umbilicaris

4c. Whorls more or less flat-sided, umbilicus absent or chink-like .........................................................................5

5a. Shell rarely exceeding 3 mm, prosocline growth lines .............................. Odostomia turrita

5b. Shell rather pointed, not exceeding 3.5 mm, orthocline growth lines ........................ Odostomia plicata

5c. Shell a more or less broad cone, periphery slightly keeled ...............................................................................6

6a. Shell not exceeding 5 mm, prosocline growth lines, periphery usually distinctly keeled Odostomia unidentata

6b. Shell not exceeding 3.5 mm, very broad cone, protoconch completely exposed .... Odostomia cf. turgida