Notodiscus Hookeri
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''Notodiscus hookeri'' is a
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
of small air-breathing
land snail A land snail is any of the numerous species of snail that live on land, as opposed to the sea snails and freshwater snails. ''Land snail'' is the common name for terrestrial molluscs, terrestrial gastropod mollusks that have gastropod shell, shel ...
, a
terrestrial Terrestrial refers to things related to land or the planet Earth, as opposed to extraterrestrial. Terrestrial may also refer to: * Terrestrial animal, an animal that lives on land opposed to living in water, or sometimes an animal that lives on o ...
gastropod Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and fro ...
mollusk Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000  extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The ...
in the family
Charopidae Charopidae is a Taxonomy (biology), taxonomic family (biology), family of small air-breathing land snails (and semi-slugs such as ''Otoconcha dimidiata''), terrestrial molluscs, terrestrial pulmonate gastropod mollusks in the superfamily Punctoi ...
. This snail lives on islands in the
sub-Antarctic The sub-Antarctic zone is a physiographic region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region inc ...
region. Its shell is unique among land snails in that the organic shell layers contain no
chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...
.


Taxonomy

This species was described under the name ''Helix hookeri'' by an English conchologist
Lovell Augustus Reeve Lovell Augustus Reeve (19 April 1814 – 18 November 1865) was an English conchologist and publisher. Life Born at Ludgate Hill, London, on 19 April 1814, he was the son of Thomas Reeve, draper and mercer, and Fanny Reeve, née Lovell. After ...
in 1854. The
specific name Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany), the two-part (bino ...
''hookeri'' is in honor of English botanist
Joseph Dalton Hooker Sir Joseph Dalton Hooker (30 June 1817 – 10 December 1911) was a British botanist and explorer in the 19th century. He was a founder of geographical botany and Charles Darwin's closest friend. For 20 years he served as director of the Ro ...
, who collected this snail during the Antarctic expedition led by James Clark Ross. Reeve's
type description A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...
reads in
Latin Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
and in English language as follows:
Henry Augustus Pilsbry Henry Augustus Pilsbry (7 December 1862 – 26 October 1957) was an American biologist, malacologist and carcinologist, among other areas of study. He was a dominant presence in many fields of invertebrate taxonomy for the better part of a cent ...
classified this species as ''Helix hookeri'' in 1887 or within the genus '' Amphidoxa'' as ''Amphidoxa hookeri'' within the family
Endodontidae Endodontidae is a taxonomic family of very small air-breathing land snails and slugs, terrestrial pulmonate gastropod molluscs in the superfamily Punctoidea. This family, which includes both snails and slugs, appears to have once been much mo ...
in 1894. Also
Alan Solem George Alan Solem (21 June 1931 – 26 March 1990),Coan E. V., Kabat A. R. & Petit R. E. (2009). ''2,400 years of malacology, 6th ed.'', February 15, 2009, 830 pp. + 32 pp. nnex of Collations American Malacological Society: http://www.malacologi ...
classified this species within the family Endodontidae in 1968. A subspecies ''Notodiscus hookeri heardensis''
Dell Dell Inc. is an American technology company that develops, sells, repairs, and supports personal computers (PCs), Server (computing), servers, data storage devices, network switches, software, computer peripherals including printers and webcam ...
, 1964 was recognized in
Heard Island The Territory of Heard Island and McDonald Islands (HIMI) is an Australian external territory comprising a volcanic group of mostly barren Antarctic islands, about two-thirds of the way from Madagascar to Antarctica. The group's overall land ...
.Madec L. & Bellido A. (2007). "Spatial variation of shell morphometrics in the subantarctic snail ''Notodiscus hookeri'' from Crozet and Kerguelen Islands". ''
Polar Biology ''Polar Biology'' is a monthly peer-reviewed scientific journal covering the biology of the polar regions. It is published by Springer Science+Business Media. According to the ''Journal Citation Reports'', the journal has a 2015 impact factor of 1. ...
'' 30: 1571-1578. .


Distribution

''Notodiscus hookeri'' has a wide distribution in the
sub-Antarctic The sub-Antarctic zone is a physiographic region in the Southern Hemisphere, located immediately north of the Antarctic region. This translates roughly to a latitude of between 46° and 60° south of the Equator. The subantarctic region inc ...
region. It is the only native terrestrial gastropod species found in the South Indian Ocean islands and archipelagos, and also in the
South Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
Province: South Indian Province: *
Crozet Islands The Crozet Islands (; or, officially, ''Archipel Crozet'') are a sub-Antarctic archipelago of small islands in the southern Indian Ocean. They form one of the five administrative districts of the French Southern and Antarctic Lands. History ...
. For example, ''Notodiscus hookeri'' is the only terrestrial snail among about 50 species of native invertebrates in the
Crozet Islands The Crozet Islands (; or, officially, ''Archipel Crozet'') are a sub-Antarctic archipelago of small islands in the southern Indian Ocean. They form one of the five administrative districts of the French Southern and Antarctic Lands. History ...
. *
Kerguelen Islands The Kerguelen Islands ( or ; in French commonly ' but officially ', ), also known as the Desolation Islands (' in French), are a group of islands in the subantarctic, sub-Antarctic region. They are among the Extremes on Earth#Remoteness, most i ...
*
Heard Island The Territory of Heard Island and McDonald Islands (HIMI) is an Australian external territory comprising a volcanic group of mostly barren Antarctic islands, about two-thirds of the way from Madagascar to Antarctica. The group's overall land ...
*
Prince Edward Islands The Prince Edward Islands are two small uninhabited subantarctic volcanic islands in the southern Indian Ocean that are administered by South Africa. They are named Marion Island (named after Marc-Joseph Marion du Fresne, 1724–1772) and P ...
South Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
Province: * ''Notodiscus hookeri'' is limited to
South Georgia South Georgia is an island in the Atlantic Ocean, South Atlantic Ocean that is part of the British Overseas Territories, British Overseas Territory of South Georgia and the South Sandwich Islands. It lies around east of the Falkland Islands. ...
in the
South Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for ...
Province. The type locality is the
Kerguelen Islands The Kerguelen Islands ( or ; in French commonly ' but officially ', ), also known as the Desolation Islands (' in French), are a group of islands in the subantarctic, sub-Antarctic region. They are among the Extremes on Earth#Remoteness, most i ...
. The land snail ''Notodiscus hookeri'' is not an endangered or a protected species.


Shell description

The
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...
growth does not stop on reaching sexual maturity, but decelerates considerably, with the biggest shells measuring 7.5–7.7 mm in size. Large intraspecific variations in shell
morphometrics Morphometrics (from Greek μορΦή ''morphe'', "shape, form", and -μετρία ''metria'', "measurement") or morphometry refers to the quantitative analysis of ''form'', a concept that encompasses size and shape. Morphometric analyses are co ...
have been reported for this species on Possession Island, with endemic variants being described as local adaptations to environmentally distinct islands. The shape of the
shell Shell may refer to: Architecture and design * Shell (structure), a thin structure ** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses Science Biology * Seashell, a hard outer layer of a marine ani ...
is depressed. The
umbilicus Umbilicus may refer to: *The navel or belly button *Umbilicus (mollusc), a feature of gastropod, Nautilus and Ammonite shell anatomy *Umbilicus (plant), ''Umbilicus'' (plant), a genus of over ninety species of perennial flowering plants *Umbilicus ...
is open. The width of the adult shell is up to 7.5-7.77 mm. The weight of the snail of the shell length 6.13 mm is 52.88 mg. The micro structure of the shell was analysed by Charrier et al. (2013). Their study was the first to demonstrate that gastropod shell micro structure responds to environmental heterogeneity, leading to the formation of ecophenotypes. The adults of ''Notodiscus hookeri'' have evolved into two ecophenotypes, which the authors referred as MS (mineral shell) and OS (organic shell): * The MS-ecophenotype is characterised by a thick but small mineralised shell. This ecophenotype is primarily found along the coastline, and may be associated with the presence of exchangeable calcium in the clay minerals of the soils. * The OS-ecophenotype is characterised by a thin but large organic shell. This ecophenotype is primarily found at high altitudes in the mesic and xeric fell-fields, in soils with large particles that lack clay and exchangeable calcium. Snails of the OS-ecophenotype are characterised by thinner and larger shell sizes compared to snails of the MS-ecophenotype, indicating a
trade-off A trade-off (or tradeoff) is a situational decision that involves diminishing or losing on quality, quantity, or property of a set or design in return for gains in other aspects. In simple terms, a tradeoff is where one thing increases, and anoth ...
between mineral thickness and shell size. The OS-ecophenotype has a highly flexible shell. ''Notodiscus hookeri'' has unique shell micro-scale structure among gastropods: * A dense and homogeneous organic layer is loosely attached to the upper
periostracum The periostracum ( ) is a thin, organic coating (or "skin") that is the outermost layer of the shell of many shelled animals, including molluscs and brachiopods. Among molluscs, it is primarily seen in snails and clams, i.e. in gastropods an ...
and the inner mineral layer. * In the organic layer of the shell, there is prevalence of glycine-rich
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s (
glycine Glycine (symbol Gly or G; ) is an amino acid that has a single hydrogen atom as its side chain. It is the simplest stable amino acid. Glycine is one of the proteinogenic amino acids. It is encoded by all the codons starting with GG (G ...
,
leucine Leucine (symbol Leu or L) is an essential amino acid that is used in the biosynthesis of proteins. Leucine is an α-amino acid, meaning it contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-Car ...
,
isoleucine Isoleucine (symbol Ile or I) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH form under biological conditions), an α-carboxylic acid group (which is in the depro ...
,
valine Valine (symbol Val or V) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α- amino group (which is in the protonated −NH3+ form under biological conditions), an α- carboxylic acid group (which is in the deproton ...
), and an absence of
chitin Chitin (carbon, C8hydrogen, H13oxygen, O5nitrogen, N)n ( ) is a long-chain polymer of N-Acetylglucosamine, ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is the second most abundant polysaccharide in nature (behind only cell ...
. Almost all other gastropods with reduced shells have chitin. The only other known example of the absence of chitin is the internal shell of the slug ''
Ariolimax columbianus ''Ariolimax columbianus'', the Pacific banana slug, is a species of slug found on the Pacific coast of North America. It is the second-largest species of terrestrial slug in the world, growing up to 25 centimeters (9.8 in) long. As of 2021, ...
''.


Ecology

This land snail is a gregarious species that lives under moist stones, moss and wet vegetation; however, it is also widespread in fell-field areas, which are characterised by very low vegetation cover. This snail live in relatively simple ecosystems, that is caused by harsh environmental conditions on subantarctic islands. It is a litter-dwelling species. The soil is known to be a nutrient resource for ''Notodiscus hookeri'', since this species has been found to significantly increase
calcium Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to it ...
release in solutions derived from
plant litter Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituent ...
. ''Notodiscus hookeri'' exclusively feeds on lichens such as '' Orceolina kerguelensis'', ''
Usnea taylorii ''Usnea taylorii'' is a fruticose lichen in the family Parmeliaceae. Ecology Its predators include the land snail ''Notodiscus hookeri''.Gadea, A., Le Pogam, P., Biver, G., Boustie, J., Le Lamer, A. C., Le Dévéhat, F., & Charrier, M. (2017). " ...
'' and ''
Pseudocyphellaria crocata ''Pseudocyphellaria crocata'' is a species of lichen in the family Peltigeraceae, belonging to the ascomycetes. Its predators include the land snail '' Notodiscus hookeri''.Gadea, A., Le Pogam, P., Biver, G., Boustie, J., Le Lamer, A. C., Le D ...
''.Gadea, A., Le Pogam, P., Biver, G., Boustie, J., Le Lamer, A. C., Le Dévéhat, F., & Charrier, M. (2017). "Which Specialized Metabolites Does the Native Subantarctic Gastropod ''Notodiscus hookeri'' Extract from the Consumption of the Lichens ''Usnea taylorii'' and ''Pseudocyphellaria crocata''?". ''Molecules'' 22(3): 425. ''Notodiscus hookeri'' appears as a generalist lichen feeder able to consume toxic metabolite-containing lichens. Hatchlings have a shell width of < 2.0 mm. Juveniles have a shell width of about 2.0-4.0 mm. Adults have a shell width larger than 4.0 mm. The biology of this species is poorly known.


On a stamp

''Notodiscus hookeri'' was depicted on the 2012 €0.60 French Southern and Antarctic Lands postal stamp.TF004.12
accessed 15 February 2014.


See also

* List of non-avian fauna of Heard Island and McDonald Islands


References

This article incorporates public domain text from the reference and (modified) CC-BY-4.0 text from referencesCharrier M., Marie A., Guillaume D., Bédouet L., Le Lannic J., Roiland C., Berland S., Pierre J.-S., Le Floch M., Frenot Y. & Lebouvier M. (2013). "Soil Calcium Availability Influences Shell Ecophenotype Formation in the Sub-Antarctic Land Snail, ''Notodiscus hookeri''". ''PLoS ONE'' 8(12): e84527.


External links

* Pugh P. J. A. & Scott B. (2002). "Biodiversity and biogeography of non-marine Mollusca on the islands of the Southern Ocean". ''
Journal of Natural History The ''Journal of Natural History'' is a scientific journal published by Taylor & Francis focusing on entomology and zoology. The journal was established in 1841 under the name ''Annals and Magazine of Natural History'' (''Ann. Mag. Nat. Hist.'') an ...
'' 36(8): 927-952. . * Pugh P. J. A. & Smith R. I. L. (2011). "''Notodiscus'' (Charopidae) on South Georgia: some implications of shell size, shell shape, and site isolation in a singular sub-Antarctic land snail". ''
Antarctic Science ''Antarctic Science'' is a monthly peer-reviewed scientific journal published by Cambridge University Press, focusing on all aspects of scientific research in the Antarctic. The editor-in-chief is Peter Convey (British Antarctic Survey). Previous ...
'' 23(5): 442-448. .
photo of the snail

photo of the shell
{{DEFAULTSORT:Notodiscus Hookeri Charopidae Gastropods described in 1854