We studied multiple true crabs (Brachyura) from primarily sponge and coral reefs that lived during the Jurassic and Cretaceous periods (201 to 66 million years ago). Both environments were important habitats for the evolution and biodiversity of crabs during the Late Jurassic epoch (164 to 145 million years ago). The central portion of the crabs, called the carapace, is used to study these crabs. We described one new genus and five new species. One species was named after UA Museums Research Associate Dr. Cristina Robins. Other taxa are redescribed in more detail, synonymized (four species), or reassigned (three species and two genera). After studying details of the carapace of closely and distantly related groups of crabs, we found similarities and differences among distantly related groups. The similarities in the rostrum might be a sign of their independent adaptation or convergent evolution in this context. In one case, we found very strong similarities between specimens of genera that were placed in two different superfamilies. We placed these taxa in the same family again and argue against extreme convergent evolution. We also report on a remarkably large parasitic swelling made by an isopod in one crab’s gill region, and we show the largest complete Jurassic crab carapace reported thus far.