The Ocular Morphology of the Southern Hemisphere Lamprey Mordacia mordax Richardson with Special Reference to a Single Class of Photoreceptor and a Retinal Tapetum

Mordacia mordax possesses a unique eye structure featuring a single type of rod-like photoreceptor and a specialized retinal tapetum.

• The eye has a well-differentiated avascular retina with distinct layers, including ganglion cell sublaminae and horizontal cells.
• Intermediate filaments associated with glial cells are arranged in bundles between the horizontal cell layers.
• Unlike other lamprey families, M. mordax has only one type of photoreceptor, which is rod-like.
• The photoreceptors are arranged in a hexagonal pattern and are surrounded by a tapetum that enhances light capture.
• The eye's characteristics may facilitate increased sensitivity to low light during nocturnal upstream migration.

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