Brachystomia Monterosato, 1884

Høisaeter, Tore, 2014, The Pyramidellidae (Gastropoda, Heterobranchia) of Norway and adjacent waters. A taxonomic review, Fauna norvegica 34, pp. 7-78 : 25

Brachystomia Monterosato, 1884

Type species, by subsequent designation: Odostomia rissoides Hanley, 1844 (= B. scalaris MacGillivray, 1843 ); designated by Crosse (1885); Britain.

Pyramidellids with small (<5 mm long), elongate-ovate to truncated, conical, solid shells, of not more than six whorls. No macroscopic sculpture. Columellar tooth present, though sometimes rather retracted. Protoconch medium-sized to small, intorted. Operculum (Figure 33) oligogyrous, thin, without a distinct indentation for the columellar tooth. Yellowish, internal process of moderate thickness, gradually decreasing in thickness towards the opercular edges. Tentacles triangular with tentacular pads at their tip. Pigmented mantle organ irregularly oval to circular consisting of yellow and brown patches.

In our waters four species may be included in this ‘genus’, but shell characters alone are not sufficient for verifying this. I have seen living material only of B. scalaris . Since this is the type species, it may be used for describing the soft parts, and how this genus differs from Odostomia s.s. Most authors have regarded Brachystomia as a subgroup of Odostomia , but Fretter et al. (1986), based on the submerged protoconch and lack of obvious shell sculpture singled out O. scalaris , O. eulimoides , O. carrozzai (as O. albella ) and O. lukisi as British members of Brachystomia . O. lukisi is definitely not closely related to the former three, and should be allocated its own new genus (see below). Schander (1995) includes O. eulimoides as well as O. carrozzai in Brachystomia , but without any explanation. Schander et al. (2003) operates with a clade ‘Brachystomia’ as separate from Odostomia , but did not include the type species in their analysis. The two exotic species included may or may not be closely related to our northeast Atlantic species. They did however include one of our four species, Odostomia angusta , in their analysis, and found this to belong in a clade together with four species of Odostomia s.s. Their two species of ‘Brachystomia’ were grouped with species of Parthenina , Liostomia , Jordaniella in a clade named Liostomini. This may be an indication that Odostomia angusta is not a member of Brachystomia after all, or that the specimen (from Vigo in northern Spain) sequenced by Schander et al. was misidentified. Key to the species of Brachystomia , based on shell morphology

1a. Whorls tumid, subsutural shelf distinct

................... Brachystomia scalaris 1b. Whorls less tumid, subsutural shelf inconspicuous ........2

2a. Body whorl occupying at least two thirds of total

.............. Brachystomia eulimoides 2b. Body whorl less dominating ............................................3

3a. Height of aperture less than 40% of shell height ................. Brachystomia carrozzai

3b. Height of aperture more than 45% of shell height ................... Brachystomia angusta