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The compound eye of true crabs have evolved into various types, corresponding to this group’s (Brachyura) broad range of lifestyles, including habitat preference, activity patterns, and feeding strategy. Even so, the origin and evolutionary development of the visual systems of Brachyura remain rather unknown. The eyes and visual systems of most extant taxa of crabs are understudied, while those of fossil specimens are rarely preserved and unavailable for examination. In this publication, authors present and describe the first example of preservation of various eye structures including the external corneal lenses, corneagenous cells, and internal retinotopic neuropils of a 95–90 mya, exceptionally preserved fossil crab, *Callichimaera perplexa*, excavated from the Cretaceous Lagerstätte of Colombia, South America. The exceptional preservation of the fossil crab and its compound eyes, allowed for a comprehensive comparison of the visual system of *C. perplexa* to those of various extant crabs, along with anatomical and ontogenetic details, by applying scanning electron microscopy (SEM). In an attempt to interpret the habitat and lifestyle of the fossil crab specimen, authors studied the relationship between eye growth rate and habitat of various extant crab taxa. The ecology, habitat and eye growth of 14 selected extant species of brachyuran crabs were compared to the preserved eye structures of the examined *C. perplexa*. For this interpretation, authors extracted depth records for benthic and pelagic occurrences of extant species from the OBIS database. The results from the extracted depth data, along with various statistical and morphological comparisons between the eyes of the fossil crab examined and those of various extant taxa, allowed for a lifestyle interpretation of the fossil crab, *C. perplexa*. The high visual acuity of the latter species, in combination with its morphologically specialised swimming legs, led to the interpretation that *C. perplexa* was an active visual swimming crab, similar to extant predator crabs in well-lit marine environments. It is hypothesised that *C. perplexa* was an active predator of pelagic comma shrimp (Cumacea), which is regularly found in masses associated with *C. perplexa* specimens..
Reference: Jenkins, K. M., Briggs, D. E., & Luque, J. (2022). The remarkable visual system of a Cretaceous crab. Iscience, 25(1), 103579. https://doi.org/10.1016/j.isci.2021.103579