Osedax

''Osedax'' is a genus of deep-sea siboglinid polychaetes, commonly called boneworms, zombie worms, or bone-eating worms. ''Osedax'' is Latin for "bone-eater". The name alludes to how the worms bore into the bones of whale carcasses to reach enclosed lipids, on which they rely for sustenance. They utilize specialized root tissues for bone-boring. It is possible that multiple species of ''Osedax'' reside in the same bone. ''Osedax'' worms are also known to feed on the collagen itself by making holes in the whale's skeletal structure. These holes can also serve as a form of protection from nearby predators.

Scientists from the Monterey Bay Aquarium Research Institute using the submarine ROV ''Tiburon'' first discovered the genus in Monterey Bay, California, in February 2002. The worms were found living on the bones of a decaying gray whale in the Monterey Canyon, at a depth of .

Anatomy and physiology

Lacking stomach and mouth, ''Osedax'' rely on symbiotic species of bacteria that aid in the digestion of whale proteins and lipids and release nutrients that the worms can absorb. ''Osedax'' have colorful feathery plumes that act as gills and unusual root-like structures that absorb nutrients. The ''Osedax'' secrete acid (rather than rely on teeth) to bore into bone to access the nutrients. High concentrations of carbonic anhydrase are found in the roots of ''Osedax.'' This serves as evidence of a common bioerosion mechanism in which secreted acid is produced by anaerobic respiration. This process works with a demineralization mechanism in which oxygen is carried from seawater to the roots and HCO3- is secreted into the seawater. Between 50 and 100 microscopic dwarf males live inside the tube surrounding a single female and never develop past the larval stage.

Through the use of X-ray CT technology, scans showed that borings made by ''Osedax mucofloris'' were hemi-ellipsoidal in shape, flat at the top, and a bit rounded at the deepest point within the bone. The borings’ surface area to volume ratio decreases as the borings become larger due to the hemi-ellipsoidal shape. Boring depths varied depending on which specific bone was colonized by the ''O. mucofloris''. Higher boring depths were found in radius bone compared to the ulna and vertebrae.

''Osedax'' worms have different regions such as a trunk region, ovisac region, and root region. The epidermis also plays key roles in bone deterioration and nutrient uptake. This process of bone deterioration occurs through a symbiotic relationship with an endosymbiotic bacteria. The cells in the epidermis of the ''Osedax'' root region are responsible for the secretion of digestive enzymes. The epidermis also has an expanded microvillus border which causes the ''Osedax'' worm to have a greater surface area.

Osedax roots are covered by a mucus sheath that helps protect the worm's trunk. Some studies support the theory that this sheath plays a role in dissolving the bone. This sheath could also play an important role in reducing the damage to Osedax skin by absorbing harmful acid. Another potential function of the mucus sheath is that it could inhibit the breakdown of the worm's bone matrix. This is significant because the bone matrix is integral in maintaining the worm's position while in direct contact with a bone.

Reproduction

Female ''Osedax'' worms have been observed spawning both in the wild and in laboratory aquaria (Rouse et al., 2009). ''Osedax rubiplumus'' can spawn hundreds of oocytes at a time. They are already fertilized when they're released from the female worm. The worms' endosymbionts, species of bacteria in the order Oceanospirillales, were not observed in the spawned oocytes, which suggests that they are acquired after the worms settle on the bones. In the adult, the bacteria are localised in the root-like structures that grow into the whale bone. This worm appears to be highly fecund and reproduces continuously. This may help explain why ''Osedax'' is such a diverse genus, despite the rarity of whale falls in the ocean.

Male ''Osedax'' are microscopic dwarfs that live as "harems" inside the lumen of the gelatinous tube that surrounds each female. An individual female can house hundreds of these males in her tube.

Following its discovery in 2002 by researchers at the Monterey Bay Aquarium Research Institute, the genus was announced in ''Science'' in 2004.

In late 2005, an experiment by Swedish marine biologists resulted in the discovery of a species of the worm in the North Sea off the west coast of Sweden. In the experiment, a minke whale carcass that had been washed ashore had been sunk to a depth of and monitored for several months. Biologists were surprised to find that, unlike the previous discoveries, the new species, colloquially known as "bone-eating snot flower" after its scientific name (''Osedax mucofloris''), lived in relatively shallow waters.

In November 2009, researchers reported finding as many as 15 species of boneworms living in Monterey Bay on the California coast.

Niche

The role of ''Osedax'' in the degradation of marine vertebrate remains controversial. Some scientists think that ''Osedax'' is a specialist on whalebones while others think that it is more of a generalist. This controversy is due to a biogeographic paradox: despite the rarity and ephemeral nature of whale falls, ''Osedax'' has a broad biogeographic range and is surprisingly diverse. One hypothesis advanced to explain this paradox is that ''Osedax'' are able to colonize a variety of vertebrate remains besides whalebones. This hypothesis is supported by an experiment involving cow bones suspended above the sea floor. A variety of ''Osedax'' species successfully colonized these bones. ''Osedax'' have also been observed colonizing terrestrial mammal bones mixed in with galley waste from a surface vessel. Other scientists have countered this hypothesis by pointing out how the cow bone experiment does not match any natural habitat and also the low probability of terrestrial mammal bones arriving at the ocean floor in significant quantities. They also point out other cases of food falls in which the remains disappeared too swiftly for ''Osedax'' colonization and the lack of any observed colonization in similar cases. The true role of ''Osedax'' in the degradation of marine vertebrate remains is important to marine vertebrate taphonomy. Burrows closely similar to those made by ''Osedax'' species have been found in the bones of ancient marine birds and plesiosaurs, suggesting that the genus may once have had a wider range of foods. In a study of the boring morphological diversity of Osedax, it was shown that the species difference of bone-boring is highly variable; within the same species, the boring morphology is only consistent in a particular bone, but not consistent in different bones. It was also suggested that multiple species of Osedax can co-exist in the same bone and in an incomplete spatial niche differentiation.

The function of ''Osedax'' and their borings welcome other species such as '' Stephonyx'' amphipods, '' Paralomis'' crabs, and '' Rubyspira'' gastropods. As ''Osedax'' worms break down bone and lipid layers, fauna take advantage and colonize these bone matrices. Overall, the borings made by ''Osedax'' have shown to enhance biodiversity and the worms should, therefore, be considered ecosystem engineers. The downside of the deterioration caused by ''Osedax'' is that it speeds up the process of erosion, therefore only allowing this new fauna their new habitats for a temporary period.

Evolution

The oldest trace fossils on bones characteristic of ''Osedax'' are from a plesiosaur humerus from the Cambridge Greensand, England, likely reworked from late Albian (~100 million years old) sediments and a rib and costal plate from a sea turtle found in Cenomanian (100-93 million years ago) aged sediments of the Chalk Group, England. ''Osedax'' likely persisted on the bones of sea turtles after the extinction of most large marine reptiles at the end of the Cretaceous. ''Osedax'' have the generalist ability to feed on different vertebrates (fishes, marine birds, whale bones).

In terms of evolutionary history research, the ''Osedax'' could have had negative impact in preserving fossil record because its appearance at the shelf-depth combined with its ability to efficiently break down marine vertebrates skeletons.

Species

Selected species:Fujikura, Fujiwara & Kawato. ZOOLOGICAL SCIENCE 23: 733–740 (2006)
* '' Osedax antarcticus'' Glover, Wiklund & Dahlgren, 2013
* ''Osedax braziliensis'' Fujiwara, Jimi, Sumida, Kawato, Kitazato
* ''Osedax bryani'' Rouse, Goffredi, Johnson & Vrijenhoek
* '' Osedax crouchi'' Amon, Wiklund, Dahlgren, Copley, Smith, Jamieson & Glover, 2014
* '' Osedax deceptionensis'' Taboada, Cristobo, Avila, Wiklund & Glover, 2013
* ''Osedax docricketts'' Rouse, Goffredi, Johnson & Vrijenhoek
* '' Osedax frankpressi'' Rouse, Goffredi & Vrijenhoek, 2004
* ''Osedax jabba'' Rouse, Goffredi, Johnson & Vrijenhoek
* '' Osedax japonicus'' Fujikura, Fujiwara & Kawato, 2006
* ''Osedax knutei'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax lehmani'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax lonnyi'' Rouse, Goffredi, Johnson & Vrijenhoek
* '' Osedax mucofloris'' Glover, Kallstrom, Smith & Dahlgren, 2005
* '' Osedax nordenskjoeldi'' Amon, Wiklund, Dahlgren, Copley, Smith, Jamieson & Glover, 2014
* '' Osedax priapus'' Rouse et al., 2014
* ''Osedax packardorum'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax randyi'' Rouse, Goffredi, Johnson & Vrijenhoek
* '' Osedax rogersi'' Amon, Wiklund, Dahlgren, Copley, Smith, Jamieson & Glover, 2014
* ''Osedax roseus'' Rouse, Worsaae, Johnson, Jones & Vrijenhoek, 2008
* '' Osedax rubiplumus'' Rouse, Goffredi & Vrijenhoek, 2004
* ''Osedax ryderi'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax sigridae'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax talkovici'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax tiburon'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax ventana'' Rouse, Goffredi, Johnson & Vrijenhoek
* ''Osedax westernflyer'' Rouse, Goffredi, Johnson & Vrijenhoek

References

Further reading

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External links

Press release describing discovery of ''Osedax''

BBC website
– link to story about discovery of ''Osedax'' worms in the North Sea


* ttps://www.theguardian.com/environment/2022/aug/22/discovered-in-the-deep-the-worm-that-eats-bones-osedax Discovered in the deep: the worm that eats bones– The Guardian

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Sabellida