Vitrina alaskana vs. pellucida, and V. limpida vs. angelicae?
The genus Vitrina is just one of several genera of snails in the family Vitrinidae, which is most speciose in the western Palaearctic. Here in North America, there is just one genus represented by a couple of species. Henry Pilsbry (1946) knew the North American Vitrina species as V. limpida Gould, 1850 and V. alaskana Dall, 1905. A third species, V. angelicae Beck, 1837, was said to be exclusively to Greenlandic, and all of these names continue to be used by some. It is unclear to me why this usage persists but may have been the (relative) obscurity of a work in German in a foreign journal (although not in any way an obscure one) that was simply overlooked or ignored for many years. In the “historical” literature, Vitrina limpida was said to occur across North America, east of the Rockies, and west of those same mountains, Vitrina alaskana. This seems simple enough, but the species names and the artificial (unproven) pseudo-biogeographic separation of them is incorrect. To aid in this discussion, the species will initially be referred to as the “eastern” and “western” species but knowing that the Rockies are not the boundary between the two.
To begin, Pilsbry’s (1946) species accounts for the eastern and western Vitrina species are not sufficient to identify the species. There are few places in his descriptions that hint at the actual differences between the species, but to be fair, Pilsbry just did not have enough data available. The first “modern” treatment of some species of Vitrina was by a Swiss malacologist, Lothar Forcart (1955). He provided the first clear differences between the reproductive anatomy of V. pellucida and V. angelicae. In V. pellucida the penis and vas deferens are enclosed by a sheath of connective tissue and the base of the bursa copulatrix duct is rather broad. Vitrina angelicae lacks the penial sheath and the duct of the bursa copulatrix is slender throughout. Recently, Giusti et al. (2011) corroborated these differences.
The “eastern” species: Forcart (1955) also found that the V. limpida of eastern North America is the same species as V. angelicae from Greenland; material from both of these areas had the same reproductive anatomy and differed from examples of European V. pellucida. However, he regarded the eastern North American populations as subspecifically distinct on what now seem trivial differences. In his comparison of these taxa, Forcart wrote that the anatomy of V. a. limpida was the same as that of V. a. angelicae but compared the relative shell sizes, remarking that shells with the same number of whorls were larger in angelicae than in limpida. I have not seen Greenlandic material myself, but aside from the supposed size difference, there does not appear to be any substantial differences between Greenland and North American snails and subspecies seem unwarranted. Is geography alone justification for subspecies? Perhaps not. Pilsbry (1946) also noted this size difference (was Forcart merely reiterating Pilsbry?) and on page 505 doubted that V. angelicae is a valid species. (Size in itself seems variable, at least in the “western” species, and may be related to habitat suitability.) If we accept that subspecies have merit, then the “eastern” species in North America should go by the name Vitrina angelicae limpida. If not, then it would be V. angelicae, which is my preference.
The “western” species: Forcart (1955) did not have any material of Vitrina alaskana available to him for his study, could not comment on it, and so he provisionally retained the species. Afterwards, the reproductive anatomy of V. alaskana remained unknown for almost another two decades until Walter Miller, who was aware of Forcart’s publication, dissected Arizona and Montana animals (Bequaert & Miller 1973). Miller found that the reproductive anatomy was the same as expected for V. pellucida. That is, the penial sheath was present and the duct of the bursca copulatrix (spermathecal duct in his parlance) was swollen at its base. They wrote (1973: 74), “Accordingly, alaskana should be treated as a subspecies of V. pellucida, kept as such only for convenience as the American offshoot of a Pleistocene immigrant from Eurasia …”. Again, is geography alone sufficient for recognizing subspecies?
Roth & Sadeghian (2003) stressed that no differences have been demonstrated and they formally synonymized the Vitrina alaskana with V. pellucida. I have to agree with them. Should a subspecies (or species) name be retained “for convenience” only? My studies of British Columbia and Alberta specimens have verified that (so far) only V. pellucida occurs in these provinces (Forsyth 2004; unpublished).
Species ranges: So how far east does Vitrina pellucida extend? And how far west does V. angelicae occur? Do the ranges of these species overlap? Those questions are unanswerable at this time … mostly. All British Columbia animals that I have studied are V. pellucida, as are Alberta individuals. Included is an animal from Cypress Hills in the southeast corner of Alberta; that would put this as the most eastern verified record of V. pellucida in Canada. Vitrina pellucida is almost certainly in the Saskatchewan part of the Cypress Hills, but is it on the Plains?
Unfortunately, I have no material available to me from the “great malacological gap” of the Canadian Prairie Provinces of Saskatchewan and Manitoba. Determining the east–west extends of these species’ ranges will have to wait ….
- Bequaert, J.C., and Miller, W.B. 1973. The Mollusks of the Arid Southwest with an Arizona Checklist. Tucson: University of Arizona Press. xiv + 271 pp.
- Forcart, L. 1955. Die nordischen Arten der Gattung Vitrina. Archiv für Molluskenkunde 85 (4/6): 155–166, pl. 12.
- Forsyth, R.G. 2004. Land Snails of British Columbia, Royal BC Museum Handbook. Victoria: Royal British Columbia Museum. iv, 188 pp.,  col. pl.
- Giusti, F., Fiorentino, V., Benocci, A., and Manganelli, G. 2011. A survey of vitrinid land snails (Gastropoda: Pulmonata: Limacoidea). Malacologia 53 (2): 279–363.
- Pilsbry, H.A. 1946. Land Mollusca of North America (north of Mexico), Volume 2, Part 1. The Academy of Natural Sciences of Philadelphia, Monographs 3: frontispiece + i–vi, 1–520.
- Roth, B., and Sadeghian, P.S. 2003. Checklist of the land snails and slugs of California. Santa Barbara Museum of Natural History Contributions in Science 3: 1–81.