The ocelli of Archaeognatha, or jumping bristletails, differ from typical insect ocelli in shape and field of view. While the shape of the lateral ocelli is highly variable among species, most Machiloidea have sole shaped lateral ocelli beneath the compound eyes and a median ocellus that is oriented downward. This study investigated morphological and physiological aspects of the ocelli of Machilis hrabei and Lepismachilis spp.
The light reflecting ocellar tapetum in Machilis hrabei is made up by xanthine nanocrystals, as demonstrated by confocal Raman spectroscopy. Pigment granules in the photoreceptor cells move behind the tapetum in the dark adapted state. Such a vertical pigment migration in combination with a tapetum has not been described for any insect ocellus so far. The pigment migration has a dynamic range of around 4 log units and is maximally sensitive to green light. Adaptation from darkness to bright light lasts over an hour, which is slow compared to the radial pupil mechanism in some dragonflies and locusts.
- Received March 31, 2016.
- Accepted July 18, 2016.
- © 2016. Published by The Company of Biologists Ltd