Scaly-foot gastropod
Scaly-foot / Sea pangolin | |
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Chrysomallon squamiferum from Longqi. Scale bar is 1 cm | |
Scientific classification ![]() | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Mollusca |
Class: | Gastropoda |
Subclass: | Neomphaliones |
Order: | Neomphalida |
Family: | Peltospiridae |
Genus: | Chrysomallon Chen, Linse, Copley & Rogers, 2015 |
Species: | C. squamiferum
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Binomial name | |
Chrysomallon squamiferum Chen, Linse, Copley & Rogers, 2015[2]
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Synonyms[2] | |
Crysomallon squamiferum (orth. error) |
Chrysomallon squamiferum,
The shell is of a unique construction, with three layers; the outer layer consists of
The snail's
Taxonomy
This species was first discovered in April 2001, and has been referred to as the "scaly-foot" gastropod since 2001.[8] It has been referred to as Chrysomallon squamiferum since 2003, but it was not formally described in the sense of the International Code of Zoological Nomenclature until Chen et al. named it in 2015.[2][9] Type specimens are stored in the Natural History Museum, London.[2] During the time when the name was not yet formalized, an incorrect spelling variant was "Crysomallon squamiferum".[2]
Chrysomallon squamiferum is the
Distribution
![Bathymetric map of southeastern Indian Ocean showing three localities.](http://upload.wikimedia.org/wikipedia/commons/thumb/1/1d/Chrysomallon_squamiferum_map_2.png/370px-Chrysomallon_squamiferum_map_2.png)
The scaly-foot gastropod is a vent-endemic gastropod known only from the deep-sea hydrothermal vents of the Indian Ocean, which are around 2,780 metres (1.73 mi) in depth.
Peltospiridae snails are mainly known to live in Eastern Pacific vent fields. Nakamura et al. hypothesized that the occurrence of the scaly-foot gastropod in the Indian Ocean suggests a relationship of the hydrothermal vent faunas between these two areas.[14]
![](http://upload.wikimedia.org/wikipedia/commons/thumb/e/e3/Central_Indian_Ridge_hydrothermal_vents_map.png/370px-Central_Indian_Ridge_hydrothermal_vents_map.png)
Research expeditions have included:
- 2000 – an expedition of the
- 2001 – an expedition of the U.S. research vessel RV Knorr with ROV Jason discovered scaly-foot gastropods in the Kairei vent field.[8]
- 2007 – an expedition of RV Da Yang Yi Hao discovered the Longqi vent field.[2]
- 2009 – an expedition of RV Yokosuka with DSV Shinkai 6500 discovered the Solitaire field and sampled scaly-foot gastropods there.[14]
- 2009 – an expedition of RV Da Yang Yi Hao visually observed scaly-foot gastropods at Longqi vent field.[2][17]
- 2011 – an expedition of the British Royal Research Ship RRS James Cook with ROV Kiel 6000 sampled the Longqi vent field.[2][22]
Description
Sclerites
![A white scale of a nearly rectangular shape.](http://upload.wikimedia.org/wikipedia/commons/thumb/3/3b/Chrysomallon_squamiferum_sclerite.png/170px-Chrysomallon_squamiferum_sclerite.png)
In this species, the sides of the snail's foot are extremely unusual, being armoured with hundreds of iron-mineralised
The sclerites of C. squamiferum are mainly proteinaceous (conchiolin is a complex protein); in contrast, the sclerites of chitons are mainly calcareous.[18] There are no visible growth lines of conchiolin in cross-sections of sclerites.[18] No other extant or extinct gastropods possess dermal sclerites,[18] and no other extant animal is known to use iron sulfides in this way, either in its skeleton,[2] or exoskeleton.
The size of each sclerite is about 1 × 5 mm in adults.
In life, the external surfaces of sclerites host a diverse array of epibionts: Campylobacterota (formerly Epsilonproteobacteria) and Thermodesulfobacteriota (formerly part of Deltaproteobacteria).[26] These bacteria probably provide their mineralization.[26] Goffredi et al. (2004) hypothesized that the snail secretes some organic compounds that facilitate the attachment of the bacteria.[26]
Shell
![Apertural views of three globose shells with the foot covered by scales. The right shell is white with white scales, while two shells are dark with dark scales.](http://upload.wikimedia.org/wikipedia/commons/thumb/0/00/Three_populations_of_Chrysomallon_squamiferum.jpg/220px-Three_populations_of_Chrysomallon_squamiferum.jpg)
Kairei, Longqi, Solitaire (left to right)
The shell of these species has three whorls.[2] The shape of the shell is globose and the spire is compressed.[2] The shell sculpture consists of ribs and fine growth lines.[2] The shape of the aperture is elliptical.[2] The apex of the shell is fragile and it is corroded in adults.[2]
This is a very large peltospirid compared to the majority of other species, which are usually below 15 millimetres (3⁄5 in) in shell length.[2] The width of the shell is 9.80–40.02 mm (0.39–1.58 in);[2] the maximum width of the shell reaches 45.5 millimetres (1.79 in).[2] The average width of the shell of adult snails is 32 mm.[2] The average shell width in the Solitaire population was slightly less than that in the Kairei population.[15] The height of the shell is 7.65–30.87 mm (0.30–1.22 in).[2] The width of the aperture is 7.26–32.52 mm (0.29–1.28 in).[2] The height of the aperture is 6.38–27.29 mm (0.25–1.07 in).[2]
The shell structure consists of three layers. The outer layer is about 30 μm thick, black, and is made of iron sulfides, containing greigite Fe3S4.[27] This species is the only extant animal known to feature this material in its skeleton.[2] The middle layer (about 150 μm) is equivalent to the organic periostracum which is also found in other gastropods.[27] The periostracum is thick and brown.[2] The innermost layer is made of aragonite (about 250 μm thick), a form of calcium carbonate that is commonly found both in the shells of molluscs and in various corals.[27] The color of the aragonite layer is milky white.[2]
Each shell layer appears to contribute to the effectiveness of the snail's defence in different ways. The middle organic layer appears to absorb mechanical strain and energy generated by a squeezing attack (for example by the claws of a crab), making the shell much tougher. The organic layer also acts to dissipate heat.[28] Features of this composite material are in focus of researchers for possible use in civilian and military protective applications.[27]
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Two varieties of scaly-foot gastropod
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C. squamiferum from the Kairei vent field
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C. squamiferum from the Solitaire vent field
Operculum
In this species, the shape of the operculum changes during growth, from a rounded shape in juveniles to a curved shape in adults.[14] The relative size of the operculum decreases as individuals grow.[5] About a half of all adult snails of this species possess an operculum among the sclerites at the rear of the animal.[14] It seems likely that the sclerites gradually grow and fully cover the whole foot for protection, and the operculum loses its protective function as the animal grows.[14]
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A juvenile with operculum indicated by the red pointer. The shell length is about 2 mm.
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An operculum of a juvenile snail. The scale bar is 1 mm.
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An operculum of an adult snail. The scale bar is 1 mm.
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Adult snails with operculum indicated by red arrowheads. The scale bar is 5 mm.
External anatomy
![Black-and-white image showing two tentacles around a snout. There is a big ctenidium above them. The ctenidium has an appearance like a double-sided comb.](http://upload.wikimedia.org/wikipedia/commons/thumb/f/f6/Chrysomallon_squamiferum_7.png/220px-Chrysomallon_squamiferum_7.png)
sn – snout,
tt – cephalic tentacle.
The scale bar is 2 mm.
The scaly-foot gastropod has a thick snout, which tapers distally to a blunt end. The mouth is a circular ring of muscles when contracted and closed.[5] The two smooth cephalic tentacles are thick at the base and gradually taper to a fine point at their distal tips.[5] This snail has no eyes.[5] There is no specialised copulatory appendage.[5] The foot is red and large, and the snail cannot withdraw the foot entirely into the shell.[2] There is no pedal gland in the front part of the foot.[5] There are also no epipodial tentacles.[5]
Internal anatomy
In C. squamiferum, the soft parts of the animal occupy approximately two whorls of the interior of the shell.
The
In the excretory system, the nephridium is central, tending to the right side of the body, as a thin dark layer of glandular tissue.[5] The nephridium is anterior and ventral of the digestive gland, and is in contact with the dorsal side of the foregut.[5]
The
The ctenidium provides oxygen for the snail, but the circulatory system is enlarged beyond the scope of other similar vent gastropods.[5] There are no endosymbionts in or on the gill of C. squamiferum.[5] The enlargement of the gill is probably to facilitate extracting oxygen in the low-oxygen conditions that are typical of hydrothermal-vent ecosystems.[5]
At the
ct – ctenidium,
pm – pedal muscle,
sc – scales,
si – blood sinus,
te – testis.
The scale bar is 1 cm.
The scaly-foot gastropod is a chemosymbiotic
The nervous system is large, and the brain is a solid neural mass without ganglia.[5] The nervous system is reduced in complexity and enlarged in size compared to other neomphaline taxa.[5] As is typical of gastropods, the nervous system is composed of an anterior oesophageal nerve ring and two pairs of longitudinal nerve cords, the ventral pair innervating the foot and the dorsal pair forming a twist via streptoneury.[5] The frontal part of the oesophageal nerve ring is large, connecting two lateral swellings.[5] The huge fused neural mass is directly adjacent to, and passes through, the oeosophageal gland, where the bacteria are housed.[5] There are large tentacular nerves projecting into the cephalic tentacles.[5] The sensory organs of the scaly-foot gastropod include statocysts surrounded by the oesophageal gland, each statocyst with a single statolith.[5] There are also sensory ctenidial bursicles on the tip of the gill filaments; these are known to be present in most vetigastropods, and are present some neomphalines.[5]
The
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It is hypothesized that the derived strategy of housing endosymbiotic microbes in an oesophageal gland, has been the catalyst for anatomical innovations that serve primarily to improve the fitness of the bacteria, over and above the needs of the snail.[5] The great enlargement of the oesophageal gland, the snail's protective dermal sclerites, its highly enlarged respiratory and circulatory systems and its high fecundity are all considered to be adaptations which are beneficial to its endosymbiont microbes.[5] These adaptations appear to be a result of specialisation to resolve energetic needs in an extreme chemosynthetic environment.[5]
Ecology
Habitat
This species inhabits the hydrothermal vent fields of the Indian Ocean. It lives adjacent to both acidic and reducing vent fluid, on the walls of black-smoker chimneys, or directly on diffuse flow sites.[5]
The depth of the Kairei field varies from 2,415 to 2,460 m (7,923 to 8,071 ft),
The abundance of scaly-foot gastropods was lower in the Kairei field than in the Longqi field.
The Solitaire field is at a depth of 2,606 m (8,550 ft), and its dimensions are approximately 50 by 50 m (160 by 160 ft).
![Snails with grey shell and grey scales. Red-brown annelids and yellow-white crustaceans are around.](http://upload.wikimedia.org/wikipedia/commons/thumb/6/68/Chrysomallon_squamiferum_8.png/220px-Chrysomallon_squamiferum_8.png)
The Longqi vent field is in a depth of 2,780 m (9,120 ft),
Feeding habits
The scaly-foot gastropod is an obligate
For identification of trophic interactions in a habitat, where direct observation of feeding habits is complicated, carbon and nitrogen stable-isotope compositions can be measured.[32] There are depleted values of δ13C in the oesophageal gland (relative to photosynthetically derived organic carbon).[26] Chemoautotrophic symbionts were presumed as a source of such carbon.[26] Chemoautotrophic origin of the stable carbon isotope 13C was confirmed experimentally.[29]
Tissue | δ13C | δ15N |
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Oesophageal gland | −20.7 ± 0.9 ‰ | 3.3 ± 1.8 ‰ |
Gill | −18.3 ± 0.6 ‰, from −17.4 to −18.8 ‰ | 3.9 ± 0.6 ‰, from 3.1 to 4.2 ‰ |
Mantle | from −17.5 to −18.6 ‰ | from 3.5 to 4.7 ‰ |
Foot | −18.2 ± 0.6 ‰ | 3.8 ± 0.5 ‰ |
Scales | −16.7 ± 0.6 ‰ | 3.8 ± 0.9 ‰ |
Life cycle
This gastropod is a
Conservation measures and threats
The scaly-foot gastropod is not protected.[1][20] Its potential habitat across all Indian Ocean hydrothermal vent fields has been estimated to be at most 0.27 square kilometres (67 acres), while the three known sites at which it has been found, between which only negligible migration occurs,[38] add up to 0.0177 square kilometres (4.4 acres),[1] or less than one-fifth of a football field.[20]
The population at the Longqi vent field may be of particular concern. The Southwest Indian Ridge, within which it is located, is one of the slowest-spreading
The Solitaire Vent Field falls within the
It has been listed as an endangered species in the
See also
Notes
- ^ 21 species were known from Longqi as of 2016 and two new gastropods were described in 2017.
References
- ^ . Retrieved 19 November 2021.
- ^ .
- ^ "Meet the Bizarre Sea Snail That Builds Its Own Iron Suit of Armor". 15 November 2021.
- PMID 31332328.
- ^ PMID 26085836.
- ^ "The IUCN Red List of Threatened Species". IUCN Red List of Threatened Species. Retrieved 2019-07-28.
- PMID 31337912.
- ^ S2CID 543841.)
{{cite journal}}
: CS1 maint: numeric names: authors list (link - ^ Bouchet, P. (2014). "Chrysomallon squamiferum". World Register of Marine Species. Retrieved 2015-04-22.
- ^ S2CID 38386600.
- ^ .
- ^ (in Japanese) (2010) "硫化鉄を纏わない白スケーリーフットを世界で初めて発見 ~インド洋における新規熱水探査の成果~". Japan Agency for Marine-Earth Science and Technology, University of Tokyo, Kōchi University. (press release). Retrieved 2016-07-16.
- ^ "New Scaly-Foot Gastropod found in Indian Ocean; discovery of a white scaly-foot gastropod". Southern Fried Science. 1 July 2011. Retrieved 2016-07-16.
- ^ PMID 22431990.
- ^ PMID 24358117.
- ^ ISSN 2296-7745.
- ^ doi:10.1130/G32389.1.
- ^ .
- PMID 22235194.
- ^ a b c d e f Sigwart, Julia D.; Chen, Chong; Marsh, Leigh (2017). "Is mining the seabed bad for mollusks?". The Nautilus. 131 (1): 43–49.
- ^ S2CID 85582014.
- ^ S2CID 18521717.
- ^ Pickrell, John (2003-11-07). "Armor-Plated Snail Discovered in Deep Sea". National Geographic News. Archived from the original on November 10, 2003. Retrieved 2016-07-16.
- ^ PMID 28249568.
- .
- ^ PMID 15128570.
- ^ PMID 20133823.
- ^ "Snail's iron armour eyed by military". CBC News. 2010-01-19. Retrieved 2016-07-16.
- ^ PMID 23924784.
- PMID 28416684.
- ^ ISBN 9784431548645.
- ^ S2CID 189819863.
- ^ a b c d "Extensive population of a "rare" scaly-foot gastropod discovered". Japan Agency for Marine-Earth Science and Technology, Hokkaido University, Enoshima Aquarium. 30 November 2009. Retrieved 2016-07-16.
- ^ S2CID 127157740.
- S2CID 85253352.
- ^ a b c Okutani, Takashi; Hashimoto, Jun; Sasaki, Takenori (2004). "New gastropod taxa from a hydrothermal vent (Kairei Field) in the central Indian Ocean" (PDF). Venus. 63 (1–2): 1–10. Archived from the original (PDF) on 2013-10-04.
- ^ PMID 27966649.
- ^ Sigwart, Julia D. (Winter 2017). "Deep-sea conservation and the 'scaly-foot gastropod'" (PDF). Tentacle. 25: 39–40.
External links
Media related to Chrysomallon squamiferum at Wikimedia Commons