Digest bones on the ocean floor
Discovered by MBARI in 2002
32 species, most with marked sexual dimorphism
“Roots” in the bones use bacteria to break down bone, structures like gills outside the bones take in oxygen
Missing from bones, why?
Wikipedia summary
Like other siboglinids, Osedax lacks a mouth, gut, or anus, and instead depends on colonies of endosymbiont microbes housed inside a trophosome for nutrition. Unlike other siboglinids, however, this trophosome takes the form of a vascularized root system which penatrates bone.[1][4] These microbes, of the order Oceanospirillales, produce enzymes which hydrolyze collagen from bones, yielding nutrition to the worms.[4][1][5][6][7] Osedax exhibit very drastic sexual dimorphism, with females being >20,000 times larger than males.[8] Males are paedomorphic and microscopic, inhabiting a section of the females’ trunk where they produce sperm from yolk reserves
Journal Science, 2004: Osedax: Bone-Eating Marine Worms with Dwarf Males
We describe a new genus, Osedax, and two new species of annelids with females that consume the bones of dead whales via ramifying roots. Molecular and morphological evidence revealed that Osedax belongs to the Siboglinidae, which includes pogonophoran and vestimentiferan worms from deep-sea vents, seeps, and anoxic basins. Osedax has skewed sex ratios with numerous dwarf (paedomorphic) males that live in the tubes of females. DNA sequences reveal that the two Osedax species diverged about 42 million years ago and currently maintain large populations ranging from 105 to 106 adult females.
Siboglenidae /Pplex
Siboglinidae is a family of polychaete annelid worms that includes around 100 species commonly known as tubeworms. The family name originates from Siboglinum, the first described genus, which French biologist Maurice Caullery named after the H.M.S. Siboga, the expedition vessel that collected the original specimens from the Malay Archipelago in 1914. Caullery placed this genus in the new family Siboglinidae, and this family name is now firmly established to represent worms formerly classified as the separate phyla Pogonophora (beard worms) and Vestimentifera (giant tube worms).wikipedia+3
Body Structure
Siboglinids have bodies divided into four distinct regions. The anterior cephalic lobe bears one to over 200 thin, ciliated tentacles with tiny side branches called pinnules. Behind this is a glandular forepart that secretes the chitinous tube the worm inhabits. The trunk forms the elongated main body with various annuli, papillae, and ciliary tracts, while the posterior opisthosoma is a short, segmented region with paired chaetae that anchor the animal inside its tube.gbif+1
Unique Digestive and Nutritional Features
Adult siboglinids completely lack a mouth, gut, and anus—a remarkable trait for non-parasitic animals. Instead, they rely on chemosynthetic bacteria housed in a specialized organ called the trophosome for nutrition. These endosymbiotic bacteria colonize the larvae after settlement through horizontal transmission and provide nutrients by metabolizing sulfide-rich compounds from their deep-sea environments.sciencedirect+2
Habitat and Size
These worms inhabit chitinous tubes either buried in sediment or attached to hard substrates at ocean depths ranging from 100 to 10,000 meters. Most species are less than 1 millimeter in diameter but can reach lengths of 10 to 75 centimeters. The tubes are often clustered in large colonies containing thousands of individuals at hydrothermal vents, cold seeps, and organic-rich sediments.wikipedia+1
https://academic.oup.com/book/38846/chapter/337765410
https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/siboglinidae
https://en.wikipedia.org/wiki/Siboglinidae
https://pmc.ncbi.nlm.nih.gov/articles/PMC7143560/
https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0016309
https://www.gbif.org/species/112708238
https://comptes-rendus.academie-sciences.fr/biologies/articles/10.1016/j.crvi.2008.10.007/
https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/siboglinidae
https://www.britannica.com/animal/Siboglinum-weberi
https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.793645/full
https://pmc.ncbi.nlm.nih.gov/articles/PMC3038861/
http://nathanwhelan.com/assests/Li_et_al_2016_Siboglinidae_phylogenomics.pdf
http://www.marinespecies.org/aphia.php?p=taxdetails&id=129103
https://www.vliz.be/imisdocs/publications/ocrd/136067.pdf
https://onlinelibrary.wiley.com/doi/10.1111/j.1096-0031.2004.00039.x
Palps and pinnules to extract oxygen / Pplex
The oxygen-extracting structures in Osedax are typically referred to as “palps” and “pinnules” rather than gills, though they function as the primary respiratory surfaces. The anterior crown consists of highly vascularized palps bearing numerous side branches called pinnules, which are densely ciliated and create a large surface area optimized for oxygen uptake from seawater. These elaborate branchial structures facilitate high oxygen consumption by possessing short diffusion distances and a large surface-to-volume ratio.pmc.ncbi.nlm.nih+1
The palps and pinnules are structurally analogous to the anterior branchial plumes found in vestimentiferan tubeworms. Each pinnule is largely filled by a blood cavity forming a pinnular loop that efficiently exchanges gases. The terminology reflects their morphological origin from the cephalic lobe region rather than true segmental gill structures, though functionally they serve the same respiratory purpose.pmc.ncbi.nlm.nih
The trunk epidermis plays only a minor role in gas exchange due to its thicker structure, shorter ciliary bands, and lack of obvious respiratory specializations. The oxygen absorbed at the palps is then transported via the blood vascular system to supply the highly vascularized root structure embedded in bones, where aerobic heterotrophic endosymbionts require substantial oxygen for metabolism.royalsocietypublishing+1
https://fr.pensoft.net/article/167615/
https://pmc.ncbi.nlm.nih.gov/articles/PMC3338503/
https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0140341
https://journals.asm.org/doi/10.1128/mbio.03140-22
https://en.wikipedia.org/wiki/Osedax
https://www.journals.uchicago.edu/doi/pdfplus/10.1086/BBLv220n2p128
The males are tiny! / Pplex
Osedax, commonly called bone-eating or “zombie” worms, exhibits one of the most extreme cases of sexual dimorphism in the animal kingdom, with females being over 20,000 times larger than their microscopic dwarf males. The males live inside the gelatinous tube surrounding the female’s trunk, with 50-600 males forming a “harem” within a single female.microbialmenagerie+1
Visualization of Males Inside Females
The best images documenting this remarkable reproductive arrangement come from detailed scientific microscopy studies. Research published in the journal Invertebrate Biology includes transmission electron microscopy (TEM) and fluorescence microscopy images showing sperm from dwarf males located throughout the ovarian tissue of female Osedax. The study examined four species (O. rubiplumus, O. frankpressi, O. “green palps,” and O. “yellow collar”) and used Hoechst nuclear staining to reveal sperm with their characteristic helical nuclei distributed near the ovarian ducts.scripps.ucsd+1
Light microscopy images show the males as microscopic larvae-like organisms living within the female’s tube lumen, primarily concentrated in the anterior third near the oviduct. The males remain at the larval stage, never developing into full adults, and produce sperm from yolk reserves.wikipedia+1
Reproductive Biology
The males measure only micrometers in length while females can reach several centimeters. This extreme size difference evolved because male dwarfism prevents competition with females for food and space on the limited resource of sunken bones. The sperm from these microscopic males penetrate through the thin oviduct and travel to the ovarian tissue where fertilization occurs internally. Rather than being stored in discrete structures, the sperm are found dispersed throughout the connective tissue near the ovarian ducts, in close proximity to developing oocytes.nationalgeographic+4
https://www.oceannetworks.ca/news-and-stories/stories/where-are-the-zombie-worms/
https://microbialmenagerie.com/osedax-zombie-worms-microbe-endosymbiont/
https://en.wikipedia.org/wiki/Osedax
https://scripps.ucsd.edu/news/story-bizarre-deep-sea-bone-worm-takes-unexpected-twist
https://pmc.ncbi.nlm.nih.gov/articles/PMC4285288/
https://www.nationalgeographic.com/animals/article/_zombie_-worms-mate-inside-whale-bones
http://chargedmagazine.org/2020/11/the-undersea-bone-devourer/
https://www.montereybayaquarium.org/animals/animals-a-to-z/whale-worm
https://today.ucsd.edu/story/the_story_of_a_bizarre_deep_sea_bone_worm_takes_an_unexpected_twist
https://www.mbari.org/news/a-motley-collection-of-boneworms/
https://pmc.ncbi.nlm.nih.gov/articles/PMC10984269/
https://onlinelibrary.wiley.com/doi/10.1111/ivb.12037
https://revistapesquisa.fapesp.br/en/creatures-deep/
https://www.sciencedirect.com/org/science/article/pii/S1313298919004397
https://news.uvic.ca/media-release/where-are-the-zombie-worms/
https://www.alamy.com/stock-photo/osedax-worm.html
https://www.facebook.com/groups/457674185029274/posts/1269133680549983/
