The larval eye of the deep-sea fish Cataetyx memorabilis (Teleostei, Ophidiidae)

Abstract

1. The larval eye of the deep-sea fish Cataetyx memorabilis differs from the eye of the adult in several morphological facts: Its position is lateral, the shape is circular, the diameter is 30% of the head's length. (In the adult: position of eyes is dorsal, shape of eye is oval and the main axis corresponds to 8.3 % of the head's length.) 2. Anatomically 9 different retinal layers can be distinguished in the larval eye, with the bipolar cell—and the ganglion cell layer being the widest ones. 3. Ultrastructural investigations revealed grouped photoreceptors, rod-shaped pigment granules and lipid bodies in the choroid. 4. Serial sections allowed the reconstruction of the path of the optic nerve from the anterior-ventral part of the eye to the anterior-lateral zone of the brain. 5. Despite the larval character of the absence of outer segments, the larval eye seems to be suited for life in the mesopelagial, for it shows the typical adaptations to vision in twilight zones, e.g. enlargement of eye, pupil and lens; ratio of photoreceptor- to bipolar- to ganglion cell bodies 100:20:20 (i.e. grouped photoreceptors); absence of large posterior chamber and presence of lipid particles in the choroid.