The structure and development of the pineal complex in the lanternfish Triphoturus mexicanus (family mycotphidae)

The pineal complex of the lanterfish Triphoturus mexicans was studied by light and electron microscopy. Receptor, supportive and ganglion cells were identified in the pineal end-vesicle. The presence of receptor cells and the prominent pineal window strongly suggest a photoreceptor function. Numerous unmyelinated nerve fibers were also found in the end-vesicle. These converge to form part of the pineal stalk. Two kinds of cells (Types I and II) were distinguished in the dorsal sac, which is very well developed. Type I cells are non-ciliated ependymal cells and contain large parcels of glycogen. Type II cells contain large lipid-like inclusions and a distinct band of filaments around the entire periphery of the cell. Receptor cells appear very early in the development of T. mexicanus. They seem to originate from ependymal cells lining the roof of the third ventricle.