Leaf-litter-dwelling microsnails of Prince Edward Island, Canada (Mollusca, Gastropoda, Eupulmonata)

Samples of leaf litter were collected from 22 woodland sites throughout Prince Edward Island, Canada. Eighty-two specimens belonging to 15 species of litter-dwelling land snails were recovered from 20 of the 22 samples. One-third of the species— Carychium exile H.C. Lea, 1842, Helicodiscus shimeki Hubricht, 1982, Strobilops labyrinthicus (Say, 1817), Perpolita binneyana (Morse, 1864), and Striatura ferrea Morse, 1864—were previously undocumented in the literature as occurring in PEI. Leaf-litter sampling, even in smaller quantities, is an effective method for finding the often-neglected terrestrial mollusc fauna, which is largely composed of minute species.


Introduction
The terrestrial molluscan fauna of the province of Prince Edward Island (PEI), Canada, has received little attention. The earliest mention of a terrestrial mollusc from PEI was of a larger exotic snail, Helix hortensis, now Cepaea hortensis (O.F. Müller, 1774), in a short communication by Johnson (1906) who noted one locality of this species collected by C. Ives on the island. A year later, Ives (1907) gave a popular account of six species of land snails in a newspaper article appearing in the Prince Edward Island Agriculturalist. Several years later, perhaps the most important publication on PEI land snails was published, a report by Vanatta (1914) on collections made mostly by the botanist Bayard Long of Philadelphia and donated to the Academy of Natural Sciences in that city. Vanatta recorded 24 species, including 22 snails from at least 12 separate places around PEI. From PEI, Vanatta newly described Succinea bayardi Vanatta, 1914, which Grimm (1975 would later synonymize with Succinea wilsonii I. Lea, 1864. Since these early publications, several other authors have mentioned PEI records of terrestrial molluscs, but these most often repeat the earlier records, mainly those of Vanatta (1914) : Pilsbry 1919, 1939, 1946, 1948, Dundee 1974, and Nekola and Coles 2010. La Rocque's (1953 catalogue of Canadian Mollusca also gave some indications of the PEI terrestrial mollusc fauna, but often it is not clearly stated if species had been reported from PEI, and instead, generalized ranges were reported for many species. Most recently, McAlpine and Forsyth (2014) documented the occurrence of the introduced Arianta arbustorum (Linnaeus, 1758), and Ovaska and Lepitzki (2011) reported the first observation of the native slug Philomycus flexuolaris Rafinesque, 1820 on PEI.
However, most published records of terrestrial snails from PEI are of larger species. Microsnails, under 5 mm in their greatest dimension when fully grown, have been mostly overlooked. The publication by Vanatta (1914) is notable as including a larger number of species of microsnails. Remarkably, his publication and Bayard Long's collected materials remain the sole source of information for several species.
In scientific collections, PEI specimens of terrestrial molluscs, especially the smallest species, are not particularly well represented. For microsnails, there are some incidental collections, but the majority appear to have been collected separately in the 1960s and 1970 by Ursula Grigg and F. Wayne Grimm, respectively. Their materials are now split between the Nova Scotia Museum (NSM; Halifax, Nova Scotia) and the Canadian Museum of Nature (CMN; Gatineau, Quebec). Some individual lots collected by Grigg appear to have been split between these institutions, with the latter museum showing Grigg's married name, Thomas.
Leaf-litter samples have been found to be ideal in sampling for litter-dwelling microsnails. In autumn 2014, leaf litter was sampled from 22 woodland sites throughout PEI, and here we report on the species of snail from these collections.

Study Area
Prince Edward Island, at 5,660 km 2 , is Canada smallest province. It is one of the three Maritime Provinces and lies in the Gulf of St. Lawrence between latitudes 46 and 47°N. In the Köppen-Geiger system of climate classification, PEI has a Dfb climate: humid continental climate, without dry season and warm summer (Kottek et al. 2006). However, in contrast to the mainland, summer and fall temperatures on the PEI are delayed by the cool, then warm, surrounding waters of the Gulf of St. Lawrence and Northumberland Strait (PEI 2007). The topography of the PEI consists of rolling hills in its central and eastern portions, and low-lying land in the west and along the coast (PEI 2007). The highest point on the island is only 140 m above sea level.
At the time of the first European settlement, roughly 98% of the island was forested, but by 1900 forests amounted to only 30% of their original extent with conversion of land to agriculture (PEI 2010). Much of the present-day forests on PEI have been cut at least once (PEI 2010), and while forests have in general expanded in recent decades, regenerated forests differ from the original (PEI 2010; Curley 2016).

Methods
Twenty-two leaf-litter samples from forest sites were collected in October 2014 by Mark Arsenault, Greg Ridgeway, and Barry Bain (Forests, Fish and Wildlife staff, Government of PEI) while in the field doing other work ( Fig. 1; Table 1; Appendix). Mark Arsenault coordinated the sampling, but due to a data loss, the collector of each sample is unknown. Sample locations were chosen at random throughout the day at various locations throughout PEI. The species composition of the tree stand, as noted in the Appendix, was taken from the 2010 Prince Edward Island Corporate Land Use Inventory (PEICLUI 2010).
Leaf-litter samples were randomly collected by hand. Each sample was tightly packed and approximately 1 L in volume. Geographic coordinates were obtained from a hand-held GPS receiver. Samples were frozen, then mailed to RGF, after which each sample was spread out in a shallow pan and allowed to dry at ambient temperature of a garage. Once dry, samples were sieved to remove the coarse woody debris and larger leaves. The remaining fine material was bit-by-bit viewed under a Russian МБС-10 (MBS-10) stereomicroscope and terrestrial snails extracted. In Materials examined, "spec." denotes specimen(s), which are all dry shells. After sorting and identification, this material was deposited in the New Brunswick Museum (Saint John, New Brunswick; NBM, catalogue numbers below). Other museum collections mentioned here are Nova Scotia Museum (NSM), Canadian Museum of Nature (CMNML), and Academy of Natural Sciences of Drexler University, Philadelphia, Pennsylvania (ANSP).
The higher classification (family placement and order of families) follows Bouchet et al. (2017). Specimens were identified to species using Pilsbry (1946Pilsbry ( , 1948 or literature specifically mentioned for those species in Results.

Results
Eighty-two specimens belonging to 15 species of leaflitter dwelling land snails were recovered from 20 of the 22 sampled sites (Table 1). Only samples from two sites (PEI.11 and PEI.17) contained no snails. One-third, or five species, were found that were previously not documented from PEI in the literature.  Table 1 and addition information on stand age and species is presented in the Appendix. Green areas = forested land in 2000 (2000 Forest Outline GIS data © Department of Agriculture and Forestry, Government of PEI). Table 1. Leaf-litter collection sites on Prince Edward Island. Sites are mapped in Figure 1, and information on stand age and composition at each site is given in the Appendix. Identification. This is the smallest species of terrestrial snail, when fully grown, in PEI. The shell reaches only 1.1-1.5 mm in diameter (Pilsbry 1948). The combination of small adult size, smoothish teleoconch, and microsculpture of narrow, closely spaced raised colabral threads crossed by weak spiral striae help distinguish this species from others found in this study.
Comments. This species was previously reported from province by Vanatta (1914)  Comments. This is one of the more common terrestrial snails in collections from PEI. It was previously reported from the province by Ives (1907, as Pyramidula striatella) and by Vanatta (1914, (Armbruster 1997).
Comments. Cochlicopa lubrica was previously recorded from PEI by Vanatta (1914). This is a common species, which especially abundant in disturbed habitats on the island (RGF pers. obs. Identification. Among the three species of Striatura in PEI, S. exigua is immediately recognized by its widely spaced lamellar colabral riblets. In this respect, it is superficially more like Planogyra asteriscus (Morse, 1857) (Valloniidae), which, however, has even more erect riblets and lacks spiral sculpture on the protoconch, among other characters.
Comments. This species was previously reported from PEI by Vanatta (1914) based on two records. Unpublished older records in NSM and CMNM collections, as well as the new records indicate that this is one of the most common of the litter-dwelling microsnails. Identification. This species is distinguished by its greyish colour and dull, waxy-appearing lustre; it is quite unlike the two other species of Striatura. The microsculpture lacks the strong riblets of the Striatura exigua and S. milium (Morse, 1859).

Striatura ferrea
Comments. The eight records reported here are the first from PEI; surprisingly, this species has not previously been collected from the province. It appears to be the least common of the three Striatura species on PEI, although probably not rare. It is common in New Brunswick and Nova Scotia (RGF unpubl. data). Comments. This is a common, widespread, frequently woodland-dwelling species that was previously recorded from PEI by Vanatta (1914). Surprisingly, few specimens were found in our samples.  (2020) identification key, our PEI specimens differ from E. polygyratus in their more conical and more loosely coiled spire, and from E. alderi and E. fresti in their paler, yellowish-rather than reddish-brown shells, dull rather than glossy surface, and weaker, more closely spaced colabral threads (= "sillons" of Horsáková et al. 2020). Moreover, PEI collections were from upland woods, which is the expected habitat for E. fulvus egenus, in contrast to the wetland-dwelling E. alderi and E. fresti. Mantle pigmentation, while an important diagnostic character (Horsáková et al. 2020), was not used in identifications, as shells were either dead or the animals fully desiccated.
Comments. Although Euconulus Reinhardt, 1883 was found by B. Long at Lake Verde and this material is deposited in the collection of the Academy of Natural Sciences of Philadelphia, Vanatta (1914) inexplicably did not report Euconulus from PEI.

Discussion
Leaf-litter sampling continues to be shown to be an effective means of finding microsnails that often tend to be overlooked by hand-searching in the field, as already demonstrated elsewhere in Canada (e.g., Forsyth and Lepitzki 2015). Even the relatively small samples collected in this survey were successful in finding presumably rarer species on PEI, or if not rare species, then ones that have not been previously reported from the field. Our samples were collected somewhat "blindly" but with a basic knowledge for what to collect by one of us (MAA), a non-specialist of Mollusca, while undertaking other fieldwork. The collection of leaf-litter samples for microsnails is a technique that can be used for surveying areas opportunistically, as time permits, while in the field for other purposes. Our sampling sites all had some kind of human intervention within the last century: some had been ploughed agricultural land at one time, many had been clear cut, some had been managed forest for wood extraction but never ploughed, others had been planted after cutting. The most altered habitats did not necessarily produce the fewest numbers of species. We think that our samples might have been too small to find all species present; species found or not found may be due to random chance. Also of note is that all species found are nativeno adventive species were found in our samples.
We did not find evidence of larger snails in our samples, or even juveniles of larger snails. Cepaea hortensis (O.F. Müller, 1774) is quite common in PEI but tends to be in open habitats, and species of Polygyridae are apparently absent from PEI, based on historical collections in museums. Polygyrid species are few and rather rare in neighboring provinces of Nova Scotia and New Brunswick (RGF pers. obs.). Anguispira alternata (Say, 1817) has been collected in PEI, but last in 1966, and then only from two localities: Curtain [= Courtin] Island and Heron Wood, Bedeque (NSM collection).
Nevertheless, our new data add five species not previously reported from PEI, and we anticipate that additional species will be added with the revision of collections and new field surveys. It is especially noteworthy to consider that the current survey focussed on upland wood habitats. Surveys in other places, such as marshes, fens, swamps, and other wetland habitats would almost certainly find additional, specialist species. For example, we found Euconulus fulvus egenus in our samples, but hygric habitats likely harbor one of the wetland Euconulus species, such as E. fresti Horsáková, Nekola & Horsák (see Horsáková et al. 2020), and several species of Vertigo O.F. Müller, 1774 (see Nekola et al. 2018). Additionally, anthropized habitats are expected to harbor unreported introduced gastropods.

PEI.17
This stand is on previously ploughed soils which displays as agricultural land on the 1935 aerial photo. The stand was planted with Balsam Fir in 1958. PEI.18 This mixed softwood stand dominated by Balsam Fir, Black Spruce, and Red Maple has signs of being previously cut. PEI.19 This mixed softwood stand dominated by White Spruce, Red Spruce, and Balsam Fir is greater than 17 m tall in a low riparian zone area. PEI.20 This stand is a tolerant hardwood mix with Sugar Maple and Red maple as the dominant trees with White Birch, Balsam Fir, and poplar in the mix. The stand is characteristic of a managed or second-growth forest that may have been harvested for firewood over the centuries but never ploughed. PEI.21 This intolerant mixed-wood stand is adjacent to an old agriculture field. The stand is identified as having a clear-cut origin and is a mix of Red Maple, White Spruce, Balsam Fir, White Birch, and Pin Cherry (Prunus pensylvanica).

PEI.22
This is an Eastern Larch and White Pine plantation established in 1990 on previously ploughed soils which displays as agricultural land on the 1935 aerial photo. The stand was likely established on a clear-cut as trees are evident in the 1968 aerial photo.