Tag Archives: Cerastidae

Pachnodus velutinus (Pfeiffer)

Fleece Landsnail (Pachnodus velutinus)

The Fleece Landsnail was endemic to the island of Mahé in the Seychelles; it was specialized to the moist forests on the summits of the north-western part of the island.

The species disappeared sometimes around 1994 after invasive plants began altering its habitat, especially Cinnamon Trees (Cinnamomum verum J. Presl) and Vanilla Orchids (Vanilla planifolia Andrews) which now cover large areas of former native forest.

Predation by the introduced and invasive Tailless Tenrec (Tenrec ecaudatus (Schreber)) very likely also plays a role – many snail shells are found with conspicuous bite marks caused by this small mammal. 

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The reason for this species’ extinction is often said to be due to hybridization with a congeneric species from lower elevations, the Black Landsnail (Pachnodus niger (Dufo)); however, this assumption turned out to be wrong and the putative hybrids were found to be a completely distinct species.

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Depiction from: ‘Christian R. Altaba: Extinction through Climate Change: Review of Evidence and Analysis of Two Land Snails from the Seychelles Islands. Preprints 2022, 2022100315. https://doi.org/10.20944/preprints202210.0315.v1’

https://creativecommons.org/licenses/by/4.0/

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References:

[1] Justin Gerlach: Red Listing reveals the true state of biodiversity: a comprehensive assessment of Seychelles biodiversity. Phesluma 20: 9-22. 2012
[2] Christian R. Altaba: Extinction through Climate Change: Review of Evidence and Analysis of Two Land Snails from the Seychelles Islands. Preprints 2022, 2022100315. https://doi.org/10.20944/preprints202210.0315.v1

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edited: 29.01.2024

Pachnodus ladiguensis Gerlach

La Digue Landsnail (Pachnodus ladiguensis)

The La Digue Landsnail was described in 2003; it was restricted to the island of La Digue in the Seychelles.

The species is only known from subfossil material which had been found at about 15 cm below the surface; it is believed that this snail died out shortly after the Seychelles were colonized by human settlers in the late 18th century; the most likely reason for its disappearance is thought to have been human disturbance, especially forest clearance.

The shells reach heights of about 2.7 cm; their coloration was originally mahagony brown with a dark spiral band on the middle of the body whorl and a pink tint on the columella; however, most specimens that were found are bleached, thus it is unknown if the spiral band and the pinkish columella were normal characters. [1]

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References:

[1] J. Gerlach: New terrestrial Gastropoda (Mollusca) from Seychelles. Phelsuma 11: 39-51. 2003
[2] Justin Gerlach: Red Listing reveals the true state of biodiversity: a comprehensive assessment of Seychelles biodiversity. Phesluma 20: 9-22. 2012

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edited: 29.01.2024

Pachnodus curiosus Gerlach

Curieuse Landsnail (Pachnodus curiosus)

The Curieuse Landsnail was described in 2003; it is known only from scarce subfossil material, mainly shell fragments, that were found on the island of Curieuse in the Seychelles.

The species must have gone extinct already in the early 1800s due to forest clearings and extensive forest fires.

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References:

[1] J. Gerlach: New terrestrial Gastropoda (Mollusca) from Seychelles. Phelsuma 11: 39-51. 2003
[2] Justin Gerlach: Red Listing reveals the true state of biodiversity: a comprehensive assessment of Seychelles biodiversity. Phesluma 20: 9-22. 2012

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edited: 29.01.2024