For almost two hundred years, Cerataspis monstrosa — the otherworldly looking "monster larva" pictured here — has been turning up in the guts of everything from dolphins to tuna. But for as widely known as this larval creature is, its adult counterpart has managed to remain a mystery.


Now, with the help of DNA analysis, biologists at George Washington University think they have C. monstrosa's adult identity pegged.

C. monstrosa is something of a puzzle from a biogeographical standpoint. It's regarded by marine biologists as rare, but it's been found in the guts of sea creatures all over the world. For 180 years, the monster larva has been turning up at "mid-water" depths, so-called for existing well above the sea floor, but still a fair distance beneath the ocean surface. But finding the fully matured form of sea creatures like C. monstrosa is notoriously complicated — not only do adult counterparts often look nothing like their larval forms, they can also thrive in entirely different ocean habitats. Biologists have long suspected this to be the case with C. monstrosa, but proving it by identifying its fully matured form has proven difficult.


That's where biologist Keith Crandall comes in. Previous studies had pointed to a link between C. monstrosa and a species of deep-sea shrimp called Plesiopenaeus armatus. Using DNA data collected over the course of several years, Crandall and his colleagues were able to compare multiple genes from both organisms to confirm the larva and adult are, in fact, the same species:

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"Our work demonstrates the diagnostic power of molecular systematics in instances where larval rearing seldom succeeds and morphology and habitat are not indicative of identity," write the researchers in the latest issue of the journal Ecology and Evolution.

According to Crandall, this study would have been impossible as recently as ten years ago, because the molecular and analytical tools necessary to perform this comparison just didn't exist. It's thrilling to imagine what other mysteries will be solved in the near future, as these technologies become even faster, cheaper, and more efficient.


[Ecology and Evolution]