Scientific Name: Nearctula sp.
Taxonomy Group: Molluscs
COSEWIC Range: British Columbia
COSEWIC Assessment Date and Status Change: April 2010
COSEWIC Status: Special Concern
COSEWIC Status Criteria:
COSEWIC Reason for Designation: This minute terrestrial snail species is at the northern extent of its range, and found in lowland areas around the Strait of Georgia and on southern Vancouver Island. Most individuals live on the bark of Bigleaf Maple trees and appear to have poor capacity for dispersal between trees and sites. Removal of trees and habitat degradation due to urban expansion, roads and associated infrastructure, forestry, and agriculture are the main threats.
COSEWIC History of Status Designation: Designated Special Concern in April 2010.
SARA Status: Schedule 1, Special Concern
Date of Listing (yyyy-mm-dd): 2012-06-20
Please note that this information is provided for general information purposes only. For the most up to date and accurate list of species listed under the Species at Risk Act, please see the Justice Laws Website.
The Threaded Vertigo is a minute land snail with a high, rather cylindrical shell. The shell is about 2.4–3.3 mm high, dull, dark brown, and somewhat coarsely marked with fine, parallel growth lines. Within the opening of the adult shell, there are four white denticles (tooth–like protuberances); the immature shell lacks denticles. The Threaded Vertigo is currently without a formal scientific name due to its convoluted nomenclatural history, but the validity of the species is not in question. (Updated 2017/05/25)
Distribution and Population
The global range of the species extends from southwestern British Columbia through western Washington State and Oregon to west–central California. In Canada, the species occurs on southern Vancouver Island, Saturna Island, and the Sunshine Coast on mainland British Columbia. There are 24 recent (since 1984) distribution records. On Vancouver Island, clusters of sites occur within the Capital Regional District (Victoria area), but the species is known from only scattered sites along the east coast, northward to just south of Courtenay. In the Strait of Georgia, the species is known from one site on Saturna Island. On the Sunshine Coast (B.C. mainland), it occurs at several places between Gibsons and Egmont. (Updated 2017/05/25)
In British Columbia, the snails occur in moist deciduous and mixed–wood forests at low elevations, usually below 200 m. They are often associated with Bigleaf Maples and an understory of ferns and shrubs characteristic of moist, rich sites. Older riparian forests containing groves of large maples appear to be particularly suitable. The snails are largely arboreal and encountered most frequently on trunks of maples, where they occur within crevices of grooved bark or moss mats. They are occasionally found on other deciduous trees, on fern fronds, or on the ground within the leaf litter. The snails have a patchy distribution both within and among forest stands, and aggregations occur on some trees while others are devoid of snails. (Updated 2017/05/25)
Little is known about the biology of the Threaded Vertigo, and hence information has to be extrapolated from similar, related species. Like most land snails, the Threaded Vertigo is hermaphroditic (possesses both male and female reproductive organs), but the extent of cross–fertilization is not known. In similar species, eggs are laid singly. The lifespan is probably short, two years or less. The snails hibernate in winter and probably aestivate during dry periods in summer. Movements and active dispersal are limited, but passive transport on falling leaves during windstorms is plausible. The snails have been found in small groves of trees near roadsides and busy recreational trails, suggesting that they can tolerate some habitat disturbance, provided suitable moist microhabitats remain available. (Updated 2017/05/25)
The distribution of the species coincides with densely populated and highly modified parts of British Columbia. Much of the land conversion is historical in these lowland coastal areas, but human developments continue to encroach on remaining natural areas concomitant with an expanding population. Housing developments, road building and other associated infrastructure, agriculture, and forestry are shrinking and fragmenting habitats. Most records for this species are from parks or federal lands protected from land conversion, but potential habitats on private lands throughout most of the species’ range continue to diminish. Populations in protected areas are not necessarily secure due to habitat degradation from intensive recreational or other uses, and invasion by introduced plants and animals. (Updated 2017/05/25)
More information about SARA, including how it protects individual species, is available in the Species at Risk Act: A Guide.
Provincial and Territorial Protection
PLEASE NOTE: Not all COSEWIC reports are currently available on the SARA Public Registry. Most of the reports not yet available are status reports for species assessed by COSEWIC prior to May 2002. Other COSEWIC reports not yet available may include those species assessed as Extinct, Data Deficient or Not at Risk. In the meantime, they are available on request from the COSEWIC Secretariat.
10 record(s) found.
- COSEWIC Status Reports (1 record(s) found.)
- COSEWIC Assessments (1 record(s) found.)
- Response Statements (1 record(s) found.)
- Action Plans (1 record(s) found.)
- Management Plans (1 record(s) found.)
- Orders (2 record(s) found.)
- COSEWIC Annual Reports (1 record(s) found.)
- Consultation Documents (1 record(s) found.)
- Recovery Document Posting Plans (1 record(s) found.)
COSEWIC Status Reports
Response Statement - Threaded Vertigo (2010-12-02)This minute terrestrial snail species is at the northern extent of its range, and found in lowland areas around the Strait of Georgia and on southern Vancouver Island. Most individuals live on the bark of Bigleaf Maple trees and appear to have poor capacity for dispersal between trees and sites. Removal of trees and habitat degradation due to urban expansion, roads and associated infrastructure, forestry, and agriculture are the main threats.
COSEWIC Annual Reports
COSEWIC Annual Report - 2010 (2010-09-03)Under Canada’s Species At Risk Act (SARA), the foremost function of COSEWIC is to “assess the status of each wildlife species considered by COSEWIC to be at risk and, as part of the assessment, identify existing and potential threats to the species”. During the past year, COSEWIC held two Wildlife Species Assessment Meetings and reviewed the status of 79 wildlife species (species, subspecies, populations). During the meeting of November 2009, COSEWIC assessed or reviewed the classification of the status of 28 wildlife species. COSEWIC assessed or reviewed the classification of an additional 51 wildlife species (species, subspecies and populations) during their April 2010 meeting. For species already found on Schedule 1 of SARA, the classification of 32 species was reviewed by COSEWIC and the status of the wildlife species was confirmed to be in the same category (extirpated - no longer found in the wild in Canada but occurring elsewhere, endangered, threatened or of special concern). The wildlife species assessment results for the 2009-2010 reporting period include the following: Extirpated: 6 Endangered: 39 Threatened: 16 Special Concern: 17 Data Deficient: 1 This report transmits to the Minister the status of 46 species newly classified as extirpated, endangered, threatened or of special concern, fulfilling COSEWIC’s obligations under SARA Section 24 and 25. A full detailed summary of the assessment for each species and the reason for the designation can be found in Appendix I of the attached report. Since its inception, COSEWIC has assessed 602 wildlife species in various risk categories, including 262 Endangered, 151 Threatened, 166 Special Concern and 23 Extirpated. In addition, 13 wildlife species have been assessed as Extinct. Also, to date, 46 wildlife species have been identified by COSEWIC as Data Deficient and 166 wildlife species were assessed as Not at Risk. This year has been a particularly productive year for COSEWIC’s Aboriginal Traditional Knowledge (ATK) Subcommittee. In April 2010 COSEWIC approved the Aboriginal Traditional Knowledge Process and Protocol Guidelines, providing clear and agreed principles for the gathering of Aboriginal Traditional Knowledge to carry out COSEWIC functions as required under Section 15(2) of SARA (See Appendix III of the attached report). We are grateful for the rich and enthusiastic contribution made by community elders and experts in helping the ATK Subcommittee prepare the ATK protocols.