Stylodonta unidentata 

Scope:Global
Status_ne_offStatus_dd_offStatus_lc_offStatus_nt_offStatus_vu_onStatus_en_offStatus_cr_offStatus_ew_offStatus_ex_off

Taxonomy [top]

Kingdom Phylum Class Order Family
Animalia Mollusca Gastropoda Stylommatophora Acavidae

Scientific Name: Stylodonta unidentata
Species Authority: (Holten, 1802)
Taxonomic Notes: Six subspecies of this snail are recongized:

Stylodonta unidentata unidentata (Holten, 1802)
Stylodonta unidentata sebertae Gerlach, 2003
Stylodonta unidentata pyramidata (Pfeiffer, 1841)
Stylodonta unidentata globata (Martens, 1869)
Stylodonta unidentata praslina Gerlach, 2003
Stylodonta unidentata parva Gerlach, 2003

Assessment Information [top]

Red List Category & Criteria: Vulnerable B2ab(iii) ver 3.1
Year Published: 2009
Date Assessed: 2006-01-11
Assessor(s): Gerlach, J.
Reviewer(s): Miller, R.M., Pollock, C.M. & Seddon, M.B.
Justification:
While populations of this species are stable, the species has a limited range (AOO = 87 km²; it is found in 8 locations) and there is ongoing deterioration in habitat quality throughout this range due to invasion by introduced plants, especially Cinnamomum verum.

Geographic Range [top]

Range Description:This snail species is endemic to the Seychelles. It is found on the islands of Mahé, Therèse, Conception, Silhouette, Praslin, Curieuse, La Digue and Felicite; it has become extinct on the island of St. Anne. Its total area of occupancy (AOO) is 87 km². Most of the populations on the different islands represent different subspecies; the distribution and the area of occupancy (AOO) of each is as follows:

S. u. unidentata: North Mahé, St. Anne (extinct), Therèse and Conception; AOO = 22 km²
S. u. sebertae: West Mahé; AOO = 11 km²
S. u. pyramidata: South Mahé; AOO = 22 km²
S. u. globata: Silhouette; AOO = 19 km²
S. u. praslina: Praslin and Curieuse; AOO = 8 km²
S. u. parva: La Digue; AOO = 5 km²
Countries occurrence:
Native:
Seychelles (Seychelles (main island group))
Additional data:
Estimated area of occupancy (AOO) - km2:87Continuing decline in area of occupancy (AOO):No
Extreme fluctuations in area of occupancy (AOO):NoEstimated extent of occurrence (EOO) - km2:
Continuing decline in extent of occurrence (EOO):NoExtreme fluctuations in extent of occurrence (EOO):No
Number of Locations:8Continuing decline in number of locations:No
Extreme fluctuations in the number of locations:NoLower elevation limit (metres):10
Upper elevation limit (metres):990
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:The total population size of this species has been estimated to be 7.2 million individuals, though some subspecies are much more abundant than others. The numbers of individuals of each subspecies is estimated to be:

S. u.unidentata: 145,000
S. u. sebertae: 1,000
S. u. pyramidata: 15,000
S. u. globata: 7 million
S. u. praslina: 700
S. u. parva: 50,000

This snail's populations are considered to be stable.
Current Population Trend:Stable
Additional data:
Number of mature individuals:7211700Continuing decline of mature individuals:No
Extreme fluctuations:No
Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:NoAll individuals in one subpopulation:No

Habitat and Ecology [top]

Habitat and Ecology:This snail is a terrestrial lowland forest species, found in leaf litter, and is one of the most important detritivores in the forest ecosystem. It does not lay eggs, but rather gives birth to live young.
Systems:Terrestrial
Continuing decline in area, extent and/or quality of habitat:Yes
Generation Length (years):5

Threats [top]

Major Threat(s): It is threatened on Mahé and Praslin islands by habitat degradation caused by invasive exotic plants, especially Cinnamomum verum, and predation by the Common Tenrec (Tenrec ecaudatus), a small mammal that was introduced to the Seychelles. Small-scale farming and wood plantations have threatened this snail's habitat in the past.

Conservation Actions [top]

Conservation Actions: Some populations are protected in Morne Seychellois National Park (S. u. unidentata) and Praslin National Park (S. u. praslina). The other subspecies require the protection of Mt. Sebert on Mahé island (S. u. sebertae); the La Reserve/Brullee area on Mahé island (S. u. pyramidata); Silhouette island (S. u. globata); and the summit of La Digue (S. u. parva).

Classifications [top]

1. Forest -> 1.6. Forest - Subtropical/Tropical Moist Lowland
suitability: Suitable  major importance:Yes
1. Land/water protection -> 1.1. Site/area protection

In-Place Research, Monitoring and Planning
  Action Recovery plan:Yes
  Systematic monitoring scheme:No
In-Place Land/Water Protection and Management
  Conservation sites identified:Yes, over entire range
  Occur in at least one PA:Yes
  Percentage of population protected by PAs (0-100):10
  Area based regional management plan:No
In-Place Species Management
  Harvest management plan:No
  Successfully reintroduced or introduced beningly:No
  Subject to ex-situ conservation:No
In-Place Education
  Subject to recent education and awareness programmes:No
  Included in international legislation:No
  Subject to any international management/trade controls:No
2. Agriculture & aquaculture -> 2.1. Annual & perennial non-timber crops -> 2.1.2. Small-holder farming
♦ timing: Past, Unlikely to Return ♦ scope: Minority (<50%) ♦ severity: Negligible declines ⇒ Impact score: Past Impact 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation

2. Agriculture & aquaculture -> 2.2. Wood & pulp plantations -> 2.2.1. Small-holder plantations
♦ timing: Past, Unlikely to Return ♦ scope: Minority (<50%) ♦ severity: Negligible declines ⇒ Impact score: Past Impact 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation

8. Invasive & other problematic species & genes -> 8.1. Invasive non-native/alien species -> 8.1.2. Named species (Cinnamomum verum)
♦ timing: Ongoing ♦ scope: Whole (>90%) ♦ severity: Negligible declines ⇒ Impact score: Medium Impact: 6 
→ Stresses
  • 1. Ecosystem stresses -> 1.2. Ecosystem degradation

8. Invasive & other problematic species & genes -> 8.1. Invasive non-native/alien species -> 8.1.2. Named species (Tenrec ecaudatus)
♦ timing: Ongoing ♦ scope: Whole (>90%) ♦ severity: Negligible declines ⇒ Impact score: Medium Impact: 6 
→ Stresses
  • 2. Species Stresses -> 2.1. Species mortality

Bibliography [top]

Gerlach, J. 2003. New terrestrial Gastropoda (Mollusca) from Seychelles. Phelsuma 11: 39-51.

Gerlach, J., Matyot, P. and Samways, M.J. 2005. Developing strategies for invertebrate conservation, the case of the Seychelles islands. Phelsuma: 9-12.

IUCN. 2009. IUCN Red List of Threatened Species (ver. 2009.2). Available at: www.iucnredlist.org. (Accessed: 3 November 2009).


Citation: Gerlach, J. 2009. Stylodonta unidentata. In: The IUCN Red List of Threatened Species 2009: e.T168106A6450480. . Downloaded on 30 June 2016.
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