Ultrastructure and histological features of the Pecten oculi of the African Swamphen (Porphyrio madagascariensis): With special focus on its SEM-EDX analysis and its migratory behaviour.

Our work is regarded as the first effort to illustrate the gross, stereo-, light-, and electron-scanning microscopic features of the pecten oculi of the diurnal African Swamphen (P. madagascariensis). The SEM-EDX elemental analysis was also applied to explain its relation to their diurnal patterns. The plicated (folded) accordion-pecten oculi had three parts: the basal, middle (15-16) pleats, and the apical. The basal parts originated from the retina, while the apical parts were united to form a thick bridge. There is a gradual increase in pigmentation from the basal part to the apical bridge, resulting in greater intensity. SEM revealed a complicated, tortuous outer surface due to the high vascularization of the pecteneal pleats; additionally, it carried a vitreopecteneal limiting membrane to separate them from the corpus vitreum. High SEM magnification revealed a great abundance of hyalocytes on the pleats' outer surface. The transverse section at the basal part showed multiple capillaries, with melanin granules predominantly located within the pigment cells surrounding the capillaries. Histologically, the highly vascular pecten oculi consisted of thin pleats with numerous pigment cells that filled the area between the blood vessels. SEM-EDX analysis revealed that oxygen was at its highest in the apical part, while carbon was at its highest in the middle and basal parts. The lowest element was magnesium in the apical and basal parts, while calcium was in the middle part. The first record of niobium was in three parts. Conclusion: The pecten oculi features of these omnivorous birds near Egyptian freshwater lakes and slow-moving rivers were linked to their adaptive feeding techniques.