Odostomia unidentata ( Montagu, 1803 )

Høisaeter, Tore, 2014, The Pyramidellidae (Gastropoda, Heterobranchia) of Norway and adjacent waters. A taxonomic review, Fauna norvegica 34, pp. 7-78 : 38-41

Odostomia unidentata ( Montagu, 1803)

Figures 63-67

Turbo unidentatus - Montagu 1803:324

Odostomia unidentata (Montagu) - Alder 1848; Forbes & Hanley 1850 -51; Jeffreys 1867; Jeffreys 1870; M. Sars 1870; Friele 1874; G.O. Sars 1878; Norman 1879; Collin 1884; Jeffreys 1884; Schneider 1886; Petersen 1888; Norman 1892; Appellöf 1897; Grieg 1897; Marshall 1900; Friele & Grieg 1901; Norman 1902; Grieg 1913, 1914; Bardarson 1920; Thiele 1928; Winckworth 1932; Fretter et al. 1986; Høisaeter 1986; van Aartsen 1987; Graham 1988; Høisaeter 1989; Smith & Heppell 1991; Schander 1995; Peñas et al. 1996; Høisaeter 2009

Chemnitzia unidentata (Montagu) - Clark 1855

Ptychostomon unidentatum (Montagu) - Kobelt 1903

Odontostomia unidentata (Montagu) - Dautzenberg & Fischer 1925

Turbonilla albella Lovén, 1847

Odostomia unidentata var. albella (Lovén) - Smith & Heppell 1991

Odostomia plicata (Montagu) - M. Sars 1859 (not O. plicata ( Montagu, 1803))

Type material: Not known.

Type locality: Salcombe Bay , Devonshire, Great Britain ( Peñas et al. 1996) .

Material seen: Norway - Skagerrak , 23 spms ; Hordaland, 3287 spms; Møre og Romsdal 6 spms; Nord-Trøndelag, 15 spms; Nordland, 163 spms, 14 shs; Troms, 3 spms.

Diagnosis: Shell: Large (to 5 mm, G.O. Sars 1878), broadly conical with flatsided whorls. Typically (but not always) with keeled body whorl. No umbilicus. Protoconch large and 90° with shell axis. Postlarvae have three spiral striae at the top of of the first teleoconch whorl, and several more on its base (Figure 65). These striae are also visible on well preserved adult shells. Soft parts: Eyes large and moderately close together. Tentacles wide and fairly short, no tentacular pads. Mentum short and inconspicuous. Foot fairly wide ending in a blunt point (Figure 64 top). Pigmented mantle organ (Figure 64 bottom), oblong blotches, yellow with brown ‘fingers’. Bluish-gray blotches, spread over the head/foot-area. Operculum: (Figure 67) of typical ‘Odostomid’ type, the size of the opercular ‘anchor’ somewhere between that of O. acuta and O. turrita .

Biology: According to Fretter et al. (1986) often common on boulders with a good growth of Pomatoceros . Like S. spiralis , O. turrita and O. striolata strongly associated with Pomatoceros- reefs, at the locality at Hillersholmen, in Raunefjorden. At the locality in Knappensundet, only a handful specimens, as opposed to the thousands of O. striolata and O. turrita , were found in samples of Pomatoceros reef. Own observations in vitro indicated that young specimens of this species, and occasionally other reef-living pyramidellids, sat on the operculum of Pomatoceros , sucking out body fluids through the branchial filaments of the polychaete.

Distribution: Reported from the entire Norwegian coast, including east Finnmark by G.O. Sars (1878). In my material 3500 specimens and 650 shells. One specimen at each of three stations in the Kvaefjord/Grovfjord/Gratangen area (c. 68°40’-45’N). Ten samples with 46 specimens in the material from Skagerrak. Otherwise evenly distributed along the coast southwards, but slightly more abundant than O. turrita in all sectors. Outside Norway it is recorded from Iceland, Faroes, the Swedish west coast, all around the British Isles and Ireland, although sparingly in the southern North Sea along the Atlantic coasts of France, Spain and Portugal and also into the western part of the Mediterranean ( Fretter et al. 1986, Peñas et al. 1996). Also known from the northwestern coast of Africa, Cape Verde Islands, the Canary Islands, Madeira and Selvagens archipelago (van Aartsen et al. 1998). Recently extended to the eastern Mediterranean (Öztürk et al. 2013).

Remarks: Generally regarded as the most widely distributed species of Odostomia s.s. in European waters. Might be confused with several other species, such as O. acuta , O. turrita , O. turgida , O. conspicua and O. umbilicaris , all with protoconchs of type A, but the protoconch (Figure 66) is larger and with first whorl relatively large compared to the next whorl. A combination of size, presence of keel on body whorl, lack of umbilicus, lead-gray blotches and characteristic pigmented mantle organ are diagnostic for this species.