The "platypus" of the crab world

Fossils show the oldest swimming crab from the age of dinosaurs.

Photography: Daniel Ocampo

Crustaceans from 95 million years ago had sharp eyes and fast swimming

With their cute big eyes, this predator looks like something from a Disney cartoon

95 million years ago, a small crab was found in the waters of what is now Colombia

Today, most adult crabs are considered bottom dwellers, and they have to forage on the bottom of the ocean because their eyes are so tiny they are practically useless

Artistic restoration of Callichimaera perplexa swimming behind comma shrimp

A new study, published in iScience, looks at this ancient crab's hallmark feature: its huge eyes that made up about 16 percent of its body

Unlike most crabs today, this creature has incredible eyesight, which helps it become an active hunter, researchers at Harvard and Yale have shown

"Although Callichimaera is the cutest and smallest crab, the overall body shape of its large eyes and unusually large paddle-like legs suggest that it may have been an active swimming predator rather than one like most crabs.

Luke has been trying to understand Callichimaera since he stumbled across it during a dig in Colombia in 2005

"It's a real fantasy," Luke said

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Based on where the fossil was found, it lived in what is now Columbia, North Africa and Wyoming
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Luke and his colleagues have collected more than 100 well-preserved specimens
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It's unclear what type of prey the crab was eating, but it was found surrounded by fossils of comma shrimp, which were about the size of a grain of rice
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Luke, who first described Callichimaera in the journal Science Advances in 2019, had visited museums regularly for several years and analyzed their crab fossils before confirming it was a new species
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In a recent paper, Luke and his colleagues analyzed seven pairs of very well-preserved Callichimaera eyes
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They also compared them to the eyes of 15 extant and extinct crab species and put together their growth sequences
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Luke and first author Kelsey Jenkins, a doctoral student at Yale University, found that of the more than 1,000 crab specimens, Callichimaera had the fastest-growing eyes—eyes that may make up 16 percent of the entire body
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That's the equivalent of a human eye the size of a football
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Usually, crabs have tiny compound eyes, located at the end of the long stalk, with a track to cover and protect them
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On the other hand, Callichimaera's compound eyes are large and have no protective eye sockets, which means they are always exposed and vulnerable
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The anatomy is pretty much a secret to its visual acuity, the researchers say
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"Furthermore, such large eyes require a lot of energy and resources to maintain," Luke said.
"
This animal must be quite vision-dependent.
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In their analysis, the researchers found that to be true
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They examined the inner soft tissue of Callichimaera's eye and found that it was closer to the eyes of bees and other large-eyed insects than the stem-like eyes of crabs
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The researchers found that the crab's eyesight was as sharp as that of dragonflies and mantis shrimps, two types of hunters with excellent vision and high efficiency
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Researchers initially thought Callichimaera was a species of giant-eyed crab, and in the final larval stage, the young crabs are free-swimming predators when their eyes are relatively large
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This was a brief phase, when the crabs matured into juveniles, the bodies outgrew the eyes, and the crabs turned into the sideways scavengers seen today
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But the analysis showed that Callichimaera was not only an adult predator, but that it also maintained the characteristics of the larval stage
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The researchers next plan to study the biomechanics of Callichimaera swimming, Luke said
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Its name translates to "the puzzlingly beautiful Chimera," and Luke said he's always amazed that the research team continues to learn about the long-dead crab
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"The animal itself is beautiful and confusing," Luke said. I call it my beautiful nightmare."