Notodiscus hookeri
| Notodiscus hookeri | |
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| A live Notodiscus hookeri is eating lichen Usnea taylorii. | |
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| Apical view of the shell of holotype of Notodiscus hookeri heardensis | |
| Scientific classification | |
| Kingdom: | |
| Phylum: | |
| Class: | |
| (unranked): | clade Heterobranchia
clade Euthyneura |
| Superfamily: | |
| Family: | |
| Genus: | |
| Species: | N. hookeri
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| Binomial name | |
| Notodiscus hookeri | |
| Synonyms | |
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Helix hookeri Reeve, 1854 | |
Notodiscus hookeri is a species of small air-breathing land snail, a terrestrial gastropod mollusk in the family Charopidae.[2] This snail lives on islands in the sub-Antarctic region. Its shell is unique among land snails in that the organic shell layers contain no chitin.
Taxonomy
[edit]This species was described under the name Helix hookeri by an English conchologist Lovell Augustus Reeve in 1854.[1] The specific name hookeri is in honor of English botanist Joseph Dalton Hooker, who collected this snail during the Antarctic expedition led by James Clark Ross.[1] Reeve's type description reads in Latin and in English language as follows:[1]
Species 1474 (Mus. Brit.)
Helix hookeri. Hel. testá mediocriter umbilicatá, orbuculari-depressá, sordidè olivaceá, subirrigulariter rugoso-striatá; spirá subplanulatá, suturis impressis; anfractibus quatuor, convexis; aperturá lunato-circulari, labro simplici.
Hooker's Helix. Shell moderately umbilicated, orbicularly depressed, dull olive, rather irregularly roughly striated; spire rather flat, with sutures impressed; whorls four, convex; aperture lunar-circular, lip simple.
Hab. Kerguelen's Land; Dr. J. D. Hooker.
A small depressed species collected by Dr. Hooker in the Antarctic Expedition of the Erebus and Terror, peculiarly characterized by the sombre olive-horny coating ofPaludina and Ampullaria.
Henry Augustus Pilsbry classified this species as Helix hookeri in 1887[3] or within the genus Amphidoxa as Amphidoxa hookeri within the family Endodontidae in 1894.[4]
Also Alan Solem classified this species within the family Endodontidae in 1968.[5]
A subspecies Notodiscus hookeri heardensis Dell, 1964[6] was recognized in Heard Island.[7]
Distribution
[edit]Notodiscus hookeri has a wide distribution in the sub-Antarctic region.[2] It is the only native terrestrial gastropod species found in the South Indian Ocean islands and archipelagos, and also in the South Atlantic Province:
South Indian Province:
- Crozet Islands.[2] For example, Notodiscus hookeri is the only terrestrial snail among about 50 species of native invertebrates in the Crozet Islands.[2]
- Kerguelen Islands[2]
- Heard Island[2]
- Prince Edward Islands[2]
South Atlantic Province:
- Notodiscus hookeri is limited to South Georgia in the South Atlantic Province.[2]
The type locality is the Kerguelen Islands.[1]
The land snail Notodiscus hookeri is not an endangered or a protected species.[2]
Shell description
[edit]
The shell growth does not stop on reaching sexual maturity, but decelerates considerably, with the biggest shells measuring 7.5–7.7 mm in size.[2]
Large intraspecific variations in shell morphometrics have been reported for this species on Possession Island,[7] with endemic variants being described as local adaptations to environmentally distinct islands.[2]
The shape of the shell is depressed. The umbilicus is open.
The width of the adult shell is up to 7.5-7.77 mm.[2] The weight of the snail of the shell length 6.13 mm is 52.88 mg.[8]
The micro structure of the shell was analysed by Charrier et al. (2013).[2] Their study was the first to demonstrate that gastropod shell micro structure responds to environmental heterogeneity, leading to the formation of ecophenotypes.[2] The adults of Notodiscus hookeri have evolved into two ecophenotypes, which the authors referred as MS (mineral shell) and OS (organic shell):[2]
- The MS-ecophenotype is characterised by a thick but small mineralised shell.[2] 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.[2]
- The OS-ecophenotype is characterised by a thin but large organic shell.[2] 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.[2] Snails of the OS-ecophenotype are characterised by thinner and larger shell sizes compared to snails of the MS-ecophenotype, indicating a trade-off between mineral thickness and shell size.[2] The OS-ecophenotype has a highly flexible shell.[2]
Notodiscus hookeri has unique[2] shell micro-scale structure among gastropods:
- A dense and homogeneous organic layer is loosely attached to the upper periostracum and the inner mineral layer.[2]
- In the organic layer of the shell, there is prevalence of glycine-rich proteins (glycine, leucine, isoleucine, valine), and an absence of chitin.[2] Almost all other gastropods with reduced shells have chitin.[2] The only other known example of the absence of chitin is the internal shell of the slug Ariolimax columbianus.[9][2]
Ecology
[edit]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.[2] This snail live in relatively simple ecosystems, that is caused by harsh environmental conditions on subantarctic islands.[8] It is a litter-dwelling species.[8]
The soil is known to be a nutrient resource for Notodiscus hookeri, since this species has been found to significantly increase calcium release in solutions derived from plant litter.[2]
Notodiscus hookeri exclusively feeds on lichens such as Orceolina kerguelensis, Usnea taylorii and Pseudocyphellaria crocata.[8] Notodiscus hookeri appears as a generalist lichen feeder able to consume toxic metabolite-containing lichens.[8]
Hatchlings have a shell width of < 2.0 mm.[2] Juveniles have a shell width of about 2.0-4.0 mm.[2] Adults have a shell width larger than 4.0 mm.[2]
The biology of this species is poorly known.[2]
On a stamp
[edit]Notodiscus hookeri was depicted on the 2012 €0.60 French Southern and Antarctic Lands postal stamp.[10]
See also
[edit]References
[edit]This article incorporates public domain text from the reference[1] and (modified) CC-BY-4.0 text from references[2][8]
- ^ a b c d e f Reeve L. A. (1854). Conchologia iconica, or, Illustrations of the shells of molluscous animals 7: Species 1474, plate 208, figure 1474.
- ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad ae af ag Charrier 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. doi:10.1371/journal.pone.0084527
- ^ Pilsbry H. A. (1887). Manual of Conchology. Second series: Pulmonata. Volume 3. Helicidae – Volume I. (2)3: page 48.
- ^ Pilsbry H. A. (1894). Manual of Conchology. Second series: Pulmonata. Volume 9. Helicidae – Volume VII. (2)9: page 39, plate 5, figure 83.
- ^ Solem A. (1968). "The subantarctic land snail, Notodiscus hookeri (Reeve, 1854) (Pulmonata, Endodontidae)". Proceedings of the Malacological Society of London 38(3): 251-266. PDF[dead link] (subscription required)
- ^ Dell R. K. (1964). "Land snails from Subantarctic Islands". Transactions and Proceedings of the Royal Society of New Zealand 11: 167-173.
- ^ a b Madec L. & Bellido A. (2007). "Spatial variation of shell morphometrics in the subantarctic snail Notodiscus hookeri from Crozet and Kerguelen Islands". Polar Biology 30: 1571-1578. doi:10.1007/s00300-007-0318-7.
- ^ a b c d e f 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. doi:10.3390/molecules22030425
- ^ Meenakshi V. R. & Scheer B. T. (1970). "Chemical studies of the internal shell of the slug, Ariolimax columbianus (Gould) with special reference to the organic matrix". Comparative Biochemistry and Physiology 34(4): 953-957. doi:10.1016/0010-406X(70)91018-2.
- ^ TF004.12, accessed 15 February 2014.
External links
[edit]
- 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 36(8): 927-952. doi:10.1080/00222930110034562.
- 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 23(5): 442-448. doi:10.1017/S0954102011000289.
- photo of the snail
- photo of the shell
