Ultrastructural and SEM-EDX Analysis Characterizations of the Pecten Oculi of the Eurasian Stone-Curlew (Burhinus oedicnemus): New Insights to Its Migratory Adaptations With Northern Egyptian Coast

Abstract

Our study represents the first attempts to describe the ultrastructure features in addition to SEM-EDX analysis of the pecten oculi of the nocturnal, visually active Eurasian stone-curlew. The present study was carried out on 10 normal pecten oculi from the migrant Eurasian stone-curlew (Burhinus oedicnemus) that was captured from the Northern Egyptian coast, Edku Lake, Edku, Behera, Egypt. The intraocular folded quadrilateral fan black pecten oculi was observed on the posteroinferior wall of the eyeball. The pecten oculi had 18–20 pleats, with narrow spaces in-between. Our SEM findings showed a tortuous, coiled pecteneal surface due to numerous blood capillaries. The apical part was oriented toward the ciliary body, but the basal part was derived from the retina, just behind the optic nerve. The outer pleat surfaces are covered by the vitreopecteneal limiting membrane, which carries numerous hyalocyte cells on the outer pleat surface. The transverse sections revealed numerous blood capillaries surrounded by numerous melanin granules. Each basal part was surrounded by a thin, elevated ridge. Our SEM-EDX analysis revealed that carbon is the highest (half percent), oxygen represents about one-third, and nitrogen is one-fifth percent of all elements. The lowest elements are sulfate at the apical part and phosphorus in the middle and basal parts. In conclusion, our findings reveal that the number of pecteneal pleats is related to the nocturnal active visual pattern and the lifestyle of this migratory bird.