Odostomia conoidea, (Brocchi, 1814)

‘Odostomia’ conoidea ( Brocchi, 1814) View in CoL

Figures 45 View Figure 45 -48

Turbo conoideus Brocchi, 1814:659 ; pl. 16, Figure 2 View Figure 2

Odostomia conoidea (Brocchi) - Forbes & Hanley 1850 - 51; Jeffreys 1867, 1870; G.O. Sars 1878; Norman 1879; Collin 1880; Jeffreys 1884; Petersen 1888; Marshall 1899; Winckworth 1932; Høisaeter 1986; Peñas et al. 1996; Høisaeter 2009; Öztürk et al. 2013

Odostomia (Megastomia) conoidea (Brocchi) - van Aartsen 1987

Megastomia conoidea (Brocchi) - Smith & Heppell 1991; Schander et al. 2003

Chemnitzia conoidea (Brocchi) - Clark 1855:422

Ptychostomon conoideum (Brocchi) - Kobelt 1903

Odontostomia conoidea (Brocchi) - Dautzenberg & Fischer 1925

Odostomia polita (Bivona, 1832) - van Aartsen 1987

Turbonilla plicata (Montagu) - Lovén 1846a, b not O. plicata ( Montagu, 1803)

Type material: In Museo civico di storia naturale di Milano ( Pinna & Spezia 1978:162, pl. 53, Figure 4 View Figure 4 ) .

Type locality: Tertiary fossil from Toscana, Italy.

Material seen: Norway - Skagerrak , 30 spms, 7 shs; Hordaland, 14 spms, 3 shs; Møre og Romsdal, 11 spms, at least 9 shs; Nord-Trøndelag, 3 spms, 4 shs; Nordland, 10 spms.

Diagnosis: Shell: ( Figure 45 View Figure 45 ) to 5 mm, milky white, almost opaque; very smooth and polished, with a glossy surface. Usually with a narrow spiral incision around the periphery of the body whorl ( Figure 45 View Figure 45 right). Protoconch (Figure 46) partly submerged in first postlarval whorl. Umbilicus usually a narrow chink, but in large specimens a deep hollow. Tooth strong and prominent. Often, but not always, with spiral ridges on inside of outer lip. Soft parts: Mentum deeply cleft and diverging. Eyes small and close together. The front of the foot strongly ciliated (Figure 47 left). Pigmented mantle organ (hard to see clearly through the shell) elongated, almost linear, reddish yellow, with numerous small, yellow-white spots in a row above the gland (Figure 47 right). Operculum: (Figure 48) of same type as O. acuta (underside not studied).

Biology: Usually found at intermediate depths, from 50-60 to 200 m. According to Fretter et al. (1986) usually in association with the starfish Astropecten irregularis . “Food. Presumably the starfish”. This needs verification, as echinoderms are not among the usual hosts for pyramidellids.

Distribution: In Norway reported from the southern and western coast by G.O. Sars (1878) and from the Bergen area by Norman (1879). In my material thirteen samples from Skagerrak, 29 specimens and an additional 54 shells, more or less evenly distributed north to Bindalsfjorden (c. 65°N). Further north nine specimens from around Bodø. A large (5.0 mm) specimen in Saltfjorden (67°10’N, 170- 90 m, Modiolula phaseolina bottom). Outside Norway it is known from the Swedish west coast, the west and south coasts of the British Isles and Ireland and further south along the Atlantic coasts of France and Spain and the Mediterranean ( Fretter et al. 1986, Peñas et al. 1996, Öztürk et al. 2013). Apparently very common in the Mediterranean, and by Öztürk et al. listed as the most abundant Odostomia distributed along the Turkish coast. By van Aartsen et al. (1998) stated to be abundant also along the coast of Mauritania and the Canary Islands.

Remarks: Best identified by the combination of the partly submerged protoconch (nucleus partly hidden by first postlarval whorl) and the spiral incision around the periphery of each whorl, in addition to the solid, glossy shell. Sufficiently different from Odostomia plicata to be placed in another genus. This is supported by the molecular analysis of Schander et al. (2003). In this analysis O. conoidea is (following van Aartsen) placed in the (sub)genus Megastomia at the outset, a decision they find to be supported by their molecular data. There is however no convincing reason to put it in the nominal genus Megastomia , which is based on Odostomia conspicua which, in my opinion is a typical Odostomia s.s. and has few traits in common with O. conoidea . According to Schander et al., O. corimbensis Schander, 1993 is another member of this genus. Yet another is O. polita (Bivona, 1832) described from Palermo, Sicily, but listed as a synonym of O. conoidea by van Aartsen (1987). A final possible congener is O. harveyi van Aartsen & Smith, 1996 from the upper slope in the northeast Atlantic, a species lacking a columellar tooth. The spiral ridges (or list like ‘teeth’) on the inside of the outer lip have been noted as an important character, and even of generic significance (distinguishing Megastomia from Odostomia s.s., see van Aartsen 1987). This character is very unreliable, however, as many shells are completely smooth inside the outer lip.