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Wonderful Creatures: the bizarre-looking marine worm with an incredibly important ecological role

Almost everyone knows what an earthworm is, but these very familiar animals are just one variation on a very rich theme that is at its most fabulously varied in the oceans. The mind-boggling appearances and lifestyles of the marine segmented worms are perfectly exemplified by this week’s animal.



Looking like an intricately folded napkin or a collection of another animal’s soft parts, parchment-tube worms are wonderfully odd. It’s actually very difficult to make out what’s what with these creatures. They don’t really have a discernible head and other easily recognized morphological landmarks are few and far between. Completely adapted to a life in marine sand and mud, the U-shaped burrow they construct—roughly the same size and shape as a banana—is essentially an extension of the worm’s body and integral to how they feed, akin to a spider and its web.




The extremely fragile parchment worm lives in a banana-shaped burrow in marine sediment, which is essentially an extension of its own body. Photo by: © Arthur Anker

The extremely fragile parchment worm lives in a banana-shaped burrow in marine sediment, which is essentially an extension of its own body. Photo by: © Arthur Anker – https://www.flickr.com/photos/artour_a/.



Out of sight, down in the sand, the body of these worms is soft, pale and very fragile, but it works beautifully in conjunction with its burrow to filter particles of edible matter from the water. By rhythmically beating some of its appendages the body of a parchment-tube worm works like a pump to drive water, laden with edible morsels, through the burrow. To actually trap the good stuff the worm has a very neat trick. Some of its winglet-like appendages form a structure reminiscent of a tiny basket-ball hoop that secretes a mucus bag, the end of which is gripped by a small, cup-like structure. As the water is pumped through the burrow, the mucus bag grows increasingly heavy with edible matter until the little cup rolls up the bag and its contents into a ball. The food cup then stretches forward to deposit the nourishing bounty into a ciliated groove, along which it is shuffled towards the animal’s waiting mouth.



Sediment dwelling segmented worms, like the parchment-tube worms, are of enormous ecological significance. They are so abundant that, collectively, they filter huge quantities of sea water to extract edible matter and churn vast amounts of marine sediment – key processes in the cycling of nutrients and energy.





In this image of a parchment-tube worm you can see the fan-like appendages that rhythmically beat to pump water through the burrow. Photo by: © Arthur Anker – https://www.flickr.com/photos/artour_a/.





Dr. Ross Piper is a zoologist and author and has recently presented on the BBC/Smithsonian TV production, Wild Burma: Nature’s Lost Kingdom, soon to be shown in the USA. You can read an interview with Ross Piper here: Animal Earth: exploring the hidden biodiversity of our planet.










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