Meet Callichimaera perplexa, Strangest Crab that Has Ever Lived

Friday, April 26, 2019

Callichimaera perplexa. Image credit: Elissa Martin, Yale Peabody Museum of Natural History.

An international team of paleontologists has found the exceptionally preserved fossilized remains of an enigmatic new type of crab, Callichimaera perplexa, which lived approximately 95 million years ago (mid-Cretaceous Period) in what are now Colombia and the United States.

Callichimaera perplexa (means ‘perplexing beautiful chimera’) was about the size of a quarter and had large and unprotected compound eyes, bent claws, leg-like mouth parts, exposed tail, and small body.

It is the earliest example of a swimming arthropod with paddle-like legs since the extinction of sea scorpions more than 250 million years ago.

“These are features typical of crab larvae from the open sea,” said team leader Dr. Javier Luque, a paleontologist at Yale University.

“This suggests that some ancient crabs may have retained a few of their larval traits into adulthood, amplified them, and developed new body architecture.”

“This is an evolutionary process called heterochrony.”

Convergent decarcinized body forms in various families of false and true crabs and convergent appendages in swimming and/or fossorial arthropods. (A to I) decarcinized crabs: (A to C) mole crabs — (A) Hippa marmorata, Taiwan, (B) Albunea occulta, Taiwan, (C) Blepharipoda occidentalis; (D) porcelain crab Euceramus panatelus, Panama; (E and F) frog crabs — (E) Raninoides benedicti, Panamá, (F) Symethis sp., Panamá; (G and H) masked burrowing crabs — (G) Corystes cassivelaunus, Belgium, (H) Jonas distinctus, Taiwan; (I) chimera crab Callichimaera perplexa, Colombia. (J to Q) Other aquatic arthropods with modified appendages for swimming and/or digging: (J) sea scorpion Eurypterus remipes, New York; (K to M) insects — (K) Cybister fimbriolatus, (L) Hesperocorixa kennicottii, (M) Notonecta undulate, last instar nymph, Alberta, Canada; (N) Munnopsis longiremis, Baja California, Mexico; (O to Q) Brachyura — (O) Orithyia sinica, China, (P) Matuta victor; (Q) Arenaeus cribrarius. Image credit: Luque et al, doi: 10.1126/sciadv.aav3875.

The ancient creature is so unique and strange that it can be considered the ‘platypus of the crab world.’

“It hints at how novel forms evolve and become so disparate through time,” Dr. Luque said.

“Usually we think of crabs as big animals with broad carapaces, strong claws, small eyes in long eyestalks, and a small tail tucked under the body.”

“Well, Callichimaera perplexa defies all of these crabby features and forces a re-think of our definition of what makes a crab a crab.”

The discovery is reported in the journal Science Advances.


J. Luque et al. 2019. Exceptional preservation of mid-Cretaceous marine arthropods and the evolution of novel forms via heterochrony. Science Advances 5 (4): eaav3875; doi: 10.1126/sciadv.aav3875