Brachystomia scalaris (MacGillivray, 1843)

Figures 30-33

Odostomia scalaris - Macgillivray, 1843:154

Odostomia scalaris Macgillivray - van Aartsen & al. 1984; van Aartsen 1987; Peñas et al. 1996; Høisaeter 2009

Odostomia (Brachystomia) scalaris (Macgillivray) - Winckworth 1932

Brachystomia scalaris (Macgillivray) - Smith & Heppell 1991

Zastoma scalaris Macgillivray - Iredale 1915

Odostomia Rissoides Hanley, 1844:18

Odostomia rissoides Hanley – Jeffreys 1848; Forbes & Hanley 1850 -51; Jeffreys 1867, 1870; M. Sars 1870; Meyer & Möbius 1872; Friele 1874; G.O. Sars 1878; Norman 1879; Collin 1880; Jeffreys 1884; Petersen 1888; Marshall 1899

Odostomia (Brachystomia) rissoides Hanley - Monterosato 1884; Høisaeter 1986

Odontostomia (Brachystomia) rissoides (Hanley) - Dautzenberg & Fischer 1925

Brachystomia rissoides (Hanley) – Ankel 1936; Fretter et al. 1986; Graham 1988; Høisaeter 1989

Ptychostomon rissoides (Hanley) - Kobelt 1903

Chemnitzia pallida (Montagu) (in part) - Clark 1855

Odostomia nitida Alder, 1844:326 - Alder 1848; Jeffreys 1859; Collin 1884

Turbonilla (Odontostomia) nitida Alder - Malm, 1861

Odostomia alba Jeffreys, 1848:337 - Forbes & Hanley 1850 -51; Jeffreys 1859

Type material: Not known.

Type locality: Aberdeen in Scotland.

Material seen: Norway - Skagerrak, 65 spms; Hordaland, 820 spms; Møre og Romsdal 3 spms; Nord-Trøndelag, 30 spms; Nordland, at least 7 shs.

Diagnosis: Shell: Brachystomia with moderately prosocline growth lines, and a turreted shell shape with quite convex whorls and deep sutures. Rounded aperture. Protoconch (Figures 30 and 31) of type C (intorted) of less than one whorl and with a clear demarcation of the beginning of the first teleoconch whorl. Soft parts: Head foot complex (Figure 32, top) white with numerous small yellow pigment spots scattered over foot and tentacles, tentacles triangular with tentacular pads, mentum slightly expanded at the tip, eyes fairly large and not particularly close together. Pigmented mantle organ (Figure 32, bottom) yellow blotch with dark brown interrupted edges, masses of white ‘bubbles’ above and an oblong custard coloured gland further up. Operculum: (Figure 33), flat with only a slight thickening under the central part, no clear indentation for the columellar tooth.

Biology: B. scalaris seems to be a typical shallow water species, rarely found deeper than 15 m in our waters. It has most frequently been encountered as an ectoparasite of Mytilus edulis, but has been reported from a number of other molluscan hosts as well as free living in shallow water (Ankel & Christensen 1963, Rasmussen 1973, Fretter et al. 1986). In my studies (Høisaeter 1989), the species was found in samples dominated by Limaria hians and Modiolus, but also in samples of Pomatoceros reefs, and finally from haptera and stipes of Laminaria hyperborea in semi-exposed and fairly protected areas. In the first and last of these it was invariably the most numerous pyramidellid species. Like B. eulimoides primarily a mollusk-feeder, but my studies indicate that it occasionally co-occurs with other pyramidellids on Pomatoceros reefs.

Distribution: Rarely recorded from Norway before 1986. Norman (1879) reports it from Raunefjorden and Osterfjorden and cites earlier reports from Oslofjorden (from Jeffreys 1870). G.O. Sars (1878) records it from Oslofjorden, the southern coast and the west coast. In my material 13 samples with 34 specimens from Skagerrak, and 705 specimens from the Espegrend area. Further north 33 specimens and 39 shells, the northernmost empty shell from southwest of Bodø (67°15’N, 50- 20 m, shell gravel, slag and small stones). A sample from a shallow water algae station (containing more than 1200 Bittium reticulatum) at Fløan, bay southeast of Stamnes (64°29’N, 3-10 m, soft bottom with Laminaria saccharina, Chorda filum and other algae) contained at least 30 B. scalaris. This is thus at present the northern limit for the species (based on living material). Outside Norway it is known from Sweden and Denmark, even the western part of the Baltic Sea, all around the North Sea, the western and southern coasts of Ireland and the British Isles, further south along the Atlantic coasts of Europe (Ankel 1936) and the western Mediterranean (Peñas et al. 1996). Van Aartsen et al. (1998) extend the distribution to Mauritania, and also cite earlier records from Madeira, the Selvagens archipelago and the Azores.

Remarks: Iredale (1915) reinstated the oldest name, O. scalaris Macgillivray, which had been replaced by O. rissoides Hanley by Jeffreys (1848). The reason for this replacement was that Jeffreys regarded all the British pyramidellids as species of Odostomia. When the group was split up into several genera, the homonymy of Melania scalaris Philippi (a synonym of Pyrgiscus jeffreysii) with O. scalaris was no longer a problem (see van Aartsen 1987).