Trilobite compound eyes with crystalline cones and rhabdoms show mandibulate affinities

Most knowledge about the structure, function, and evolution of early compound eyes is based on investigations in trilobites. However, these studies dealt mainly with the cuticular lenses and little was known about internal anatomy. Only recently some data on crystalline cones and retinula cells were reported for a Cambrian trilobite species. Here, we describe internal eye structures of two other trilobite genera. The Ordovician Asaphus sp. reveals preserved crystalline cones situated underneath the cuticular lenses. The same is true for the Devonian species Archegonus (Waribole) warsteinensis, which in addition shows the fine structure of the rhabdom in the retinula cells. These results suggest that an apposition eye with a crystalline cone is ancestral for Trilobita. The overall similarity of trilobite eyes to those of myriapods, crustaceans, and hexapods corroborates views of a phylogenetic position of trilobites in the stem lineage of Mandibulata.


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Eyes of fossil specimens (trilobites) were examined using SEM, micro-CT and synchroton CT. For comparison, the eyes of recent arthropods were analysed using histology, light microscopy, and SEM.

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Exuviae of the horseshoe crab Limulus polyphemus were collected by Gerhard Scholtz at the coast of Cold Spring Harbor. Dead specimens of the centipede stem from the teaching collection of the Humboldt-Universität zu Berlin.

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nature research | reporting summary
October 2018

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