Making a skeleton out of iron: the ‘scaly-foot gastropod’

The three known forms of Chrysomallon squamiferum, from Kairei, Longqi, Solitaire vent fields (left to right)

The three known forms of Chrysomallon squamiferum, from Kairei, Longqi, Solitaire vent fields (left to right)

Gastropod researcher Chong Chen writes:

Meet Chrysomallon squamiferum, or the ‘scaly-foot gastropod’ – the only metazoan (multi-cellular) animal capable of making a skeleton out of iron! Uniquely among gastropod molluscs it carries hundreds to thousands of scales on the foot like a suit of scale armour; these scales as well as the shell usually has a layer of iron sulfides. The function of these scales has been speculated to be protective or detoxification (by accumulation of sulfide waste), but their true function is yet unknown. As part of the iron armour is made of greigite (Fe3S4), a magnetic form of iron sulfide, this amazing animal actually sticks to strong magnets. And it also rusts. That’s right – upon contact with oxygen and water, the whole exterior slowly turns to a layer of reddish rust from metallic black.

Why doesn’t it rust in its natural environment, you may ask. Well, its environment is not exactly ordinary, either. The scaly-foot only occurs in deep-sea hydrothermal vents of Indian Ocean, more than 2500 m deep and often on ‘black smoker’ chimneys spewing out hot vent fluid exceeding 350°C. Hydrothermal vents are typically oxygen-poor environments and this might prevent the animal from rusting. The wonder doesn’t stop here – it houses endosymbiont bacteria in its enlarged oesophagus which is capable of turning chemicals in the vent fluid (poisonous to most animals) to energy, and rely on these for nutrition. So it basically keeps a food farm inside the body and does not need to feed!

Hydra, an active ‘black smoker’ vent chimney in Longqi field, Southwest Indian Ridge

Hydra, an active ‘black smoker’ vent chimney in Longqi field, Southwest Indian Ridge

With shell length that averages at around 35 mm and exceeds 45 mm in large individuals, it is a very large peltospirid snail compared to most others in the family which are below 15 mm in shell length. Originally discovered in 2001 from deep-sea hydrothermal vents of Indian Ocean, despite being a charismatic species there, it was not formally described and named until 2015. Furthermore, recent find of a white population without iron on the sclerites deepens the mystery about its sclerite formation – much more exciting secrets are waiting to be unveiled from this remarkable species!

A specimen of Chrysomallon squamiferum photographed live (Photo: David Shale)

A specimen of Chrysomallon squamiferum photographed live (Photo: David Shale)

You can watch a video of Longqi hydrothermal field featuring Chrysomallon squamiferum in their natural habitat here:

http://www.youtube.com/watch?v=y6iK19xaYJg

The longest lived animal in the world?

Arctica islandicaDr Richard Preece, Curator of Molluscs at the Museum of Zoology, writes:

There have been a number of potential contenders for this crown including Giant tortoises, large whales, Asian elephants and some reptiles and fish but none of these animals has been shown to live for more than 200 years. This is not the case with the Ocean quagog (Arctica islandica), a bivalve that frequently lives for several centuries. The oldest known specimen from Iceland was shown to have lived for 507 years. How can we be so precise about its age? The answer is that bivalves, like trees, deposit annual growth increments that can be counted and crossmatched enabling the construction of long chronologies extending back hundreds or even thousands of years. The fact that the same pattern of growth increments is recognisable within populations, and even between species, demonstrates conclusively that the bivalves are responding to identical environmental signals. Such signals include water temperature and nutrient availability, as well as other factors. Knowledge of these controlling factors enables the reconstruction of past oceanic conditions at annually-resolved resolutions, so providing critical archives for the study of climate change and variations in the position and strength of ocean currents and in water chemistry. The fact that these bivalves live so long has also attracted attention from gerontologists interested in understanding why these particular animals do not die in the usual way.

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Image courtesy of Professor James Scourse, University of Wales, Bangor

Pea Clams, genus Pisidium

© University Museum of Zoology, Cambridge 2013

Drawer of Pea Clams © University Museum of Zoology, Cambridge 2013

© University Museum of Zoology, Cambridge 2013

Individual Pea Clam © University Museum of Zoology, Cambridge 2013

Hilary Ketchum, Newton Trust Fund Project Assistant at the Museum, writes:

From 2011 to 2012 I worked at the Museum on a short term contract as a catalogue data assistant. My job was to catalogue the museum’s collection of bivalve molluscs, making an online database that could be accessed by researchers worldwide.

To finish the project in one year we worked out that I would need to catalogue one drawer of shells per day, and for eight months I met this target without much difficulty. I really enjoyed my work. I got to handle some of the museum’s most beautiful and important specimens, and found out some fascinating stories about the people who had collected them.

Then one day I came across a drawer containing hundreds of glass tubes. Inside each were tens of minute browny-green shells. This was in stark contrast to the colourful sea-shells I had been cataloguing before. The shells in the tubes belonged to a kind of freshwater bivalve of the genus Pisidium (also known as pea clams). They had been collected by a former curator at the museum who was interested in their distribution in rivers and streams. He had published numerous papers on the subject and had collected them for many years. This single drawer of specimens took me not one day, but a whole month to catalogue.

Fortunately after that, again it was plain-sailing, and I finished cataloguing all 10,000 bivalve specimens as well as another 2000 other molluscs, including the cephalopods and chitons. The catalogue is now available through the museum’s website, and visitors to the museum can see a new display all about bivalves in the Upper Gallery.

Squid, Dibranchiata

© University Museum of Zoology, Cambridge 2013

© University Museum of Zoology, Cambridge 2013

Julian Jacobs, Departmental Administrator for the Department of Zoology writes:

The specimen I would like to nominate is the little squid “dibranchiata”. I find this pale, ghostly creature quite fascinating for a number of reasons. Like all cephalopods it has an other-wordly quality. It can adapt its colouration, it has a highly developed nervous system and advanced eyes. It apparently behaves cooperatively and suggests intelligence. An alien life-form from another planet could hardly look more astonishing! And small as it may be, this creature cannot fail to make you think of its terrifying big cousins. Scaled-up, this small and delicate creature becomes a terror of the deep, a deadly hunter possessed of fearsome suckers ad beak, a match for Sperm Whales 1000m below the surface of the sea. Fictionalized portrayals in Moby Dick and Twenty Thousand Leagues Under the Sea may be exaggerated, but oddly enough their deep-water habitat has protected them from being properly filmed. So even in the age of Attenborough-style natural history filming, the squid whether large or small, retains a kind of mystery that prompts fear and wonder.

Extinct Land Snails from Henderson Island

Extinct Land Snails from Henderson Island

Two species of extinct land snail from Henderson Island© Richard Preece

Two species of extinct land snail from Henderson Island
© Richard Preece

Dr Richard Preece, Curator of Malacology here at the Museum of Zoology, writes about specimens he collected during field work to Henderson Island:

Henderson Island is an uninhabited island in the middle of the South Pacific. With an area of 37 km2, it is the largest island in the Pitcairn group, and differs markedly from the three other islands.  Henderson is a raised coral atoll reaching just over 30 m above sea-level, far lower than Pitcairn (where the Bounty mutineers settled), which is volcanic, but much higher than either Oeno or Ducie, which are both atolls with minimal surface relief.  Such uplifted atolls are not common and often support unique wildlife but many have been severely disturbed by humans causing the extinction of many species.  Henderson is so remote that it has largely escaped such disturbance, which is why it has been designated a World Heritage Site.

In 1991 I was invited to join the Sir Peter Scott Commemorative Expedition to the Pitcairn islands.  This was an international venture master-minded from Cambridge, and included a few other members of the Department of Zoology.  Our aim was essentially to undertake a detailed biological survey of this unique ecosystem, conducted by a series of specialists over a 15 month period.  I was particularly interested in the molluscs that lived there but also in the fossils from the recent past.  Henderson, being largely composed of limestone, proved to be an excellent place to study fossils, both marine shells and minute species of land snail.

The uplifted peripheral rim of Henderson surrounds a shallow central depression that once formed a lagoon.  Today the plateau of Henderson is largely covered in dense low forest, supporting several endemic species of plant and animal, but fossil clams and coral in growth position can still be found in the understorey.  On the coastal slope, a number of small caves have formed, representing periods of marine erosion at various times during the uplift of the island.  Some of these caves had been used by early Polynesians, who settled on the island for a few centuries over 500 years ago. Sediments blackened with charcoal (which could be radiocarbon-dated) containing artefacts and food debris provided clear evidence of this.  Beneath the Polynesian levels were pure white cave sediments lacking archaeology but containing abundant bones of birds and snail shells.  Most of these could be assigned to species that still occur on the island but some could not be matched up.  They included at least half a dozen of land snail, and a species of flightless pigeon, that could not be found living on the island today, despite many months of intense search.  These were all species new to science, several of which I have now described formally.  It appears that the early Polynesian settlers caused more damage than previously supposed and that Henderson is not as pristine as once thought.  It nevertheless remains a wonderful place, still supporting a range of endemic species.