Marine Life / Oddities in the Ocean / Uncategorized

Mystery of the “Deep-Sea Purple Sock”

In 1915 a strange new sea creature was discovered that resembled a “purple sock”. This creature was eventually named as Xenoturbella bocki in 1949, but no one really had any idea what this weird creature was (Westblad, 1949). Unable to clearly establish more information about the creature’s fit in the evolutionary tree or even its basic life strategies, most scientists followed the protocol for when one sock is magically lost after doing laundry, and threw the oddity into the closet and shut the door.

But today, with the marvels of modern science that allow researchers to dive deeper than ever into the sea and into their analyses of the evolutionary tree, scientists have finally found the long lost other purple socks. In a 2016 Nature paper, Dr. Greg Rouse identifies four new species of the “deep-sea purple sock” group of Xenoturbella (Rouse et al., 2016).  

more xenos

Species from the eastern Pacific (Monterey Canyon, Gulf of California, and the Monterey Submarine Canyon) between 631-2980 meters depth.

Xenoturbella are a group of extremely odd creatures. They have no brain, organs, gut, gonads, defined mouth or excretory system. Rather, they seem to be just a bundle of tissue organized by a weak nervous system and capable of limited movement by cilia (mobile hair-like structures). This may not sound exciting outright, but to researchers Xenoturbella represent an important piece of the evolutionary puzzle. Namely, this new group of species may represent one of the earliest forms of invertebrate life, providing a look at a possibly foundation branch of the family tree (Hejnol et al., 2009). Further, there appears to be a shallow and deep groups, adding complexity to a presumably simple story (Rouse et al., 2016).

xeno fam tree

Even more exciting, looking at the animal’s RNA (the messenger molecules that carry DNA’s code to the ribosomes to produce proteins), researchers are finally taking a stab at how these organisms survive. Previous work found mollusk DNA with the animals, causing early researchers to believe Xenoturbella to be related to molluscs. However, the new study finds that this DNA may not be its own DNA, leading to the hypothesis that these simple looking socks are really deep-sea predators of mollusks (Rouse et al., 2016).

Yet this raises new questions. How do they hunt? How do they feed on hard bodied mollusks without a mouth or defined organ system? Is this really the whole story, or is there a different meaning behind the discovered mollusk DNA? It looks like there is a lot more to the deep-sea purple socks after all!

Images from Rouse et al., 2016.


Hejnol, A., Obst, M., Stamatakis, A., Ott, M., Rouse, G. W., Edgecombe, G. D., et al. (2009). Assessing the root of bilaterian animals with scalable phylogenomic methods. Proceedings of the Royal Society, Series B, 276, 4261–4270.

Rouse, Greg W.; Wilson, Nerida G.; Carvajal, Jose I.; Vrijenhoek, Robert C. (2016-02-03). “New deep-sea species of Xenoturbella and the position of Xenacoelomorpha”. Nature (530): 94–97. doi:10.1038/nature1654

Westblad, E. “Xenoturbella bocki ng, n. sp., a peculiar, primitive turbellarian type.” Arkiv för zoologi 1 (1949): 11-29.





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