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Charles S. Schobert, Ivan R. Schwab, Richard R. Dubielzig; Cornea In Boney And Cartilaginous Fish: Comparative Anatomy And Phylogeny. Invest. Ophthalmol. Vis. Sci. 2012;53(14):1119.
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To compare the corneal anatomy and physiology among 13 species of fish including members of Chondrichthyes (1), Sarcopterygii (1), Chondrostei (1), and Halecostomi (10, all teleosts). We intend to examine these and other fish from our collection to determine if the variations in corneal anatomy correlate with the phylogeny as fish evolved from basal to more derived species.
Fish eyes were fixed in formalin, decalcified, embedded in paraffin. Five micron sections were cut and stained with H & E.
As lineages evolved, Gnathostomata (jawed vertebrates) radiated into the Chondrichthyes (sharks, rays and other elasmobranchs) and Teleostomi. Teleostomi radiated into the Osteichthyes which consists of two groups, Actinopterygii and Sarcopterygii. The Actinopterygii includes the Chondrostei and the Neopterygii. Sturgeons are Chondrostei, the next step after the elasmobranchs, the first bony ossification is observed in this lineage phylogenetically. The Sarcopterygii include Dipnoi (all lungfish) and all later tetrapods. The Chondrostei gave rise to the Neopterygii, which include the Holostei and the Teleostei (all teleosts). In the fish described, we attempted to cover a range of lineages. To date, we have observed a wide range of corneal structure that likely matured from the more basal to the more derived species. For example, some of the species have corneae in which the scleral and dermal cornea appears fused and indistinguishable (ie, more derived). Other specimens show a significant morphologic distinction between scleral and dermal layers, while still others show a complete separation. We also describe the unique epithelium covering the cornea in the mormyrid fishes, Stomatorhinus microps and the elephant-nosed fish, Gnathonemus petersii. Both species incorporate electric receptors in the epidermis. In the Southern Stingray, Dasyatis americana, the keratocytes are arranged in discrete lines perpendicular to the collagen fibers in the corneal stroma.
A wide range of corneal phenotypes exists in fish. These anatomical variants, likely, would have developed in response to environmental pressures and also represent phylogenic variations that may give us some additional details of the path traveled by the eye as it evolved.
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