After many popular sciences in the Cat Alliance, we have become familiar with the mysterious desert cat . From the first discovery to the basic understanding of this blue-eyed cat, there is a gap of more than a hundred years.
The species we are going to introduce today is more mysterious than desert cats. Its discovery and research are more than two hundred years apart. However, it is not as cute as a desert cat.
insect terror warning! ! !
("China on the Bite of the Tongue" tone)
After the ebb, in mangrove of the Philippines , people are looking for dead trees covered with holes. Among the ugly rotten trees, there are delicious gifts from nature. People split the wood and pulled out long white things from it, like snot. It was the delicious food they were looking for during this trip - shipworm .
01 razor clams without shells?
won't be kept in the spotlight. The shipworm is actually not as terrifying as its name. It is a general term for shellfish from the family of the marsh family. What makes unique is that it lives in wood , such as mangrove , driftwood on the sea, wooden stakes or under wooden boats. Because the whole body was hiding in the wood, its shell had degenerated to only two small pieces.
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insects are afraid to slide!
shipworm looks like a meat worm. Image source: Deplewsk/wikimedia
If you treat it as razor clams without shells , it is not difficult to understand eating shipworms.
The soft body of the shipworm has a sweet taste. Some say it looks like oysters, while others say it looks like cheese. You can carry it directly into your mouth. You can pickle it with vinegar, or you can enjoy it with vinegar, bean paste and rice. There are also folk songs singing boatworms in the Philippines.
In the decaying mangrove wood, you can find small ordinary shipworms as a flavor snack © Great Big Story / youtube
It is not easy to collect shipworms. The mangrove forests are very stuffy, and there are also thick mud that can trap people and bite bugs. Some people still enjoy collecting shipworms as rare delicacies and entertainment in boring life.
However, not every Filipino is used to this delicacy, just like not every Beijinger drinks bean juice . Some people say it looks like a snot. In fact, the Filipino name tamiluk of shipworm also means "snot".
shipworm, about 60 cm long. Photography: Takashi Tsuji
In addition to being a seafood, the lifestyle of the shipworm is also very eye-catching. Its shell has tiny, dense serrated . Driven by the adductor muscle at the back end of the body, it can grind the wood bit by bit, and punch holes in the wood, thus becoming a major disaster for destroying the ship. The devoured wood chips are stored in the enlarged cecum by shipworms. Its gills have specialized cells, raising bacteria that can hydrolyze cellulose to help it digest wood.
Shipworms will also build a house for themselves. It can secrete calcium and apply a layer of inner wall of wood tunnel that it drills out to resist dryness and deformation of wood. There are also paddle-shaped calcium flakes on both sides of its siphon, which serve as the "door" to block the hole.
shipworm has also made a great contribution in history. Inspired by shipworms, French engineer Marc Isambard Brunel proposed the shield construction method , which is the earliest prototype of the shield machine . However, at that time, it was not relying on machines, but using manpower to dig.
X-ray photo of wood drilled by shipworms. Image source: Wessex Archaeology / Flickr
02 The maggot in the shipworm
In short, the shipworm is really perfectly adapted to the creatures living in wood. But there is also an alternative among the shipworms that does not eat wood. It is the maggot spirit in the shipworm, and the mysterious master in the shipworm - giant shipworm (Kuphus polythalamiia).
Giant shipworm is known, but it is actually a bit history. In 1758, the ancestor of the scientific name, Linnai , named it.But Linnaeus believes that it is a kind of worm (a relative of polyhedral and sand silkworm ). We have always had little knowledge of giant shipworms, and could only rely on a small number of degraded shells and other wreckage, and the only complete specimen (collection in , Solomon Islands, , in 1933).
Until Daniel Distel of Boston Northeastern University and his partners saw giant shipworms in a Filipino documentary and finally found a precious living specimen in 2017.
The appearance of this thing is so weird that it exceeds Rockraft's imagination. It can grow to nearly 1.5 meters long , as thick as a baseball bat, it is the largest shipworm and the longest shell animal in . Its body is not white but black, wrapped in a calcium shell. However, if you think about it from another angle, it is a bit like coconut gray ice cream?
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Giant shipworm's body and its shell. Image source: Daniel L. Distel et al. / Proceedings of the National Academy of Sciences (2017)
A giant shipworm pours out from a calcium tunnel secreted by giant shipworms © Newsy / youtube
The giant shipworm lives in the seashores near mangroves and coral reefs, and is rich in sludge with rotten wood and plant debris. They are the only shipworms that live in the mud. Scientists later found giant shipworms in rotting driftwood and tree trunks, but they were all small (no more than 11 cm), and were probably young giant shipworms. When they grow up, they may move into the mud.
Figure ABC, giant shipworms in rotten wood, picture D, giant shipworms in sludge. Image source: Reuben Shipway et al. / The Biological Bulletin (2018)
03 "Eat the fart" monster
The strangest feature of giant shipworms is that they seem to do not eat .
Their digestive system has degenerated, the cecum has shrunk, and only trace amounts of feces can be found in the intestine. They control the adductor of the shell to weaken, the strength to grind the wood decreases, and there is no sawtooth of scraping wood chips on the shell. Moreover, the tunnels they dug in the mud were sealed with calcium shells on the inside, and they could not eat the rotten wood and other things in the mud.
In fact, giant shipworm mainly relies on gas to maintain life .
, like other shipworms, the gills of giant shipworms are inhabited by symbiotic bacteria , but they are different from other shipworm bacteria. The bacterial partners of , the , can use hydrogen sulfide , generate energy, fix carbon dioxide as organic matter, and serve as food for themselves and shipworms, just like plants use light energy.
scientific drawing of giant shipworms, the yellowish-brown part of which is home to symbiotic bacteria. Image source: Daniel L. Distel et al. / Proceedings of the National Academy of Sciences (2017)
The source of hydrogen sulfide is a rich rotten plant in the silt. Other free-living bacteria will decompose sulfate in rotten wood to produce hydrogen sulfide. By the way, hydrogen sulfide is also one of the odors of flatulence. Although the smell is not very good, it is the source of life for shipworms.
makes a living by "eating" sulfides, which is not uncommon in the biological world. The mineral-rich hot spring spewed out of the seabed - deep-sea hydrothermal , is full of bacteria that like sulfides, as well as larger organisms that feed on bacteria, including animals such as Polygonum worms, conchs, shrimps, etc. The deep-sea hydrothermal port has thus become a rare and rich environment in the barren deep sea.
Animals living next to the deep sea hydrothermal port. Image source: NOAA Photo Library / Flickr
The existence of these deep-sea “buffets” raises another question: How did these creatures evolve into eating sulfides next to the hot spring? Where do they find sulfides and start the evolution of eating sulfides? The existence of the giant shipworm in
provides important information for us to uncover this mystery. There is at least one large animal that can live on sulfides, and does not need an extremely special environment such as deep-sea hydrothermal ports.In fact, the bacterial companion of the giant shipworm is related to the bacteria at the deep-sea hydrothermal portal. The rotten wood that produces hydrogen sulfide may play the role of an springboard , allowing bacteria and other organisms to evolve in the direction of using sulfides, thus becoming one of the most bizarre "inventions" in evolutionary history.
In 2019, J. Reuben Shipway of the University of Portsmouth and his colleagues published a paper describing a shipworm Lithoredo abatanica in the Philippines. It drills holes in limestone and contains calcite particles in the intestines (of course, eating stones alone cannot obtain energy, maybe it will also eat small organisms such as green algae). This is the first type of shipworm that is known to live in stone. What will be waiting for us in the future?
limestone was riddled with holes by shipworms. Image source: Reuben Shipway et al / Proceedings of the Royal Society (2019)
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Shipworm in stone Lithoredo abatanicam13. Image source: Reuben Shipway et al / Proceedings of the Royal Society (2019)
Reference
Tsuji, Takashi. "HARVESTING AND FOOD CULTURE OF SHIPWORM TAMILUK (BACTRONOPHORUS THORACITES) IN PHILIPPINE MANGROVE FORESTS."
https://www.researchgate.net/publication/359265816_HARVESTING_AND_FOOD_CULTURE_OF_SHIPWORM_TAMILUK_BACTRONOPHORUS_THORACITES_IN_PHILIPPINE_MANGROVE_FORESTS
Shipway, J. Reuben, et al. "Observations on the life history and geographic range of the giant chemosymbiotic shipworm Kuphus polythalamius (Bivalvia: Teredinidae)." The Biological Bulletin 235.3 (2018): 167-177.
https://www.journals.uchicago.edu/doi/full/10.1086/700278
Distel, Daniel L., et al. "Discovery of chemoautotrophic symbolism in the giant shipworm Kuphus polythalamiia (Bivalvia: Teredinidae) extends wooden-steps theory." Proceedings of the National Academy of Sciences 114.18 (2017): E3652-E3658.
https://www.pnas.org/doi/10.1073/pnas.1620470114
Shipway, J. Reuben, et al. "A rock-boring and rock-ingesting freshwater bivalve (shipworm) from the Philippines." Proceedings of the Royal Society B 286.1905 (2019): 20190434.
https://royalsocietypublishing.org/doi/10.1098/rspb.2019.0434
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