Shell: Small (usually less than 2.8 mm), glossy, ivory white. Protoconch intorted, extremely flat (type C) (Figure 36). Growth lines more or less vertical. Soft parts: Tentacles short and wide, apparently without tentacular pads, eyes very close together, mentum characteristically cleft, with diverging ends. Pigmented mantle organ in two parts, long and yellow above and short oval, brownish yellow below. Operculum: with a notch at the columellar side, a ventral thickening in the middle, but no typical "anchor* of the Odostomia'-type. Frequently with corroded protoconch and corrosion marks on the whorls.

According to Fretter et al. (1986) frequently found in association with fairly large assemblages of Pomatoceros, and also with Serpula and Spirorbis. This is also the case for the material from Norway, but the association with Pomatoceros is far less strong than what was observed for 0. striolata and 0. turrita (Hoisseter 1989). Thus it was not found at the Pomatoceros-dominated substrate at the Hillersholmen locality, and the three samples at the Knappensundet locality in which it was found in highest numbers (in one sample even with higher abundance than any other pyramidellid) were all typical Limaria-Modiolus dominated samples.

Odostomia lukisi
Habitat: it lives in the infralittoral zone. It can be found in Potamoceros tubes of which it feeds on, but also in Serpula and Spirorbis.
Distribution: it can be found all over the Mediterranean. Relatively common,collected at Cannizzaro (Catania - Sicily - Italy), at 40 m depth.
Notes: shell small in sizes, subcylindrical in form, whorls more or less turrite and convex, suture broad. Typical protoconch type C, very flattened. Milk white in colour, surface tipically bright. Growth lines are orthocline. Oval in aperture, columellar tooth quite evident but smaller than in O. eulimoides. Umbilicus deep. Even juvenile specimens are recognizable due to their protoconch particularly flat-sided. Measures of adult specimens are reduced: on an average around 2-2.5 mm in height.

DISTINCTIVE FEATURES:

• Shells with a clear tooth on the columella.
• Shell surface smooth or with spiral striature.
• No (spiral) ribs.
• Inside of the outer lip smooth.
• Embryonic whorls of type C, exceedingly flat.
• Shell ivory-white with (usually) shiny surface.
• Whorls more or less rounded
* Spiral more or less turriculate.

This is not a Brachystomia s.s., as is clearly seen from the soft parts. It occupies, taxonomically, an isolated position in the Norwegian pyramidellid fauna. The population of this species in Norwegian waters may fluctuate wildly from decennium to decennium, dependent on the amount of larvae brought in with water masses of varying origin and temperature.

A southern, shallow water species, in Norway only recorded from the Espegrend area except for two shells from Skagerrak and a single older record from Floro (61°36'N) (Hoisaeter 1968). All but two specimens in my material from 11 samples from the locality in Knappensundet (Straume bridge) in Grimstadfjorden (60o19’N) (see Hoisaeter 1989). Outside Norway it is reported as occurring sparingly both in the Atlantic and the Mediterranean (van Aartsen 1987). According to Graham (1988) it is among the commonest of intertidal pyramidellids on the west coast of the British Isles and the southern Channel, but is absent from the North Sea. Reported from the western Mediterranean bv both van Aartsen et al. (1984) (Algeciras Bay) and Peñas et al. (1996). Van Aartsen et al. (1998) extend the distribution to Mauritania, the Canary' Islands, Madeira, and the Azores