Biologist Unmasks Mysterious ‘Monster Larva’

The bewildering C. monstrosa now moves from nature’s curiosity bin to the realm of shrimp. Sorry, little fella. (Photo by Darryl Felder)

In life as in fiction, monsters are rarely what they seem. And now researchers have added to the evidence an ocean oddity that sparked nearly two centuries of head scratching.

This week a team of researchers, led by GW biologist Keith Crandall, reported that a curious crustacean named Cerataspis monstrosa, a larva previously unmatched to an adult animal, is an early developmental stage of a species of deep-water shrimp, Plesiopenaeus armatus.

When the so-called “monster larva” was first found in 1828 inside the gut of a dolphin, baffled scientists described it as a “monstrous and misshapen animal,” the study authors wrote in the journal Ecology and Evolution.

The deep-sea shrimp Plesiopenaeus armatus, which a new study found to be the adult form of the “monster larva.”
(Photo by W. Pequegnat)

The issue of identifying larvae that bear no resemblance to their adult selves does arise—as Dr. Crandall told the GW Hatchet, look no further than caterpillars and butterflies. Answers sometimes can be found by allowing larvae to mature in a lab, or by their affinity for a particular habitat.

But C.monstrosa sightings are pretty rare, the researchers said—mostly it turns up only after being eaten—and as it matures the creature’s preference of habitat changes, too.

So when a lone “monster larva” recently was found in the Gulf of Mexico, the research team took the opportunity to explore the DNA evidence. Genetic comparisons of C.monstrosa and members of a family of deep-sea shrimp, which was long suspected of sharing a link, identified a “near perfect” genetic match in P. armatus, the researchers wrote.

Studies linking larvae and adults “not only aid in our understanding of biodiversity, they provide insights into the life history, distribution and ecology of an organism,” said Dr. Crandall, who arrived at GW this summer to helm the new Computational Biology Institute.

The work was funded by the National Science Foundation, the Gulf of Mexico Research Initiative and the National Oceanic and Atmospheric Administration.

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