G. Alberti & A. I. Moreno-Twose


Gerd Alberti PDF
Ana Isabel Moreno-Twose Volkswagen Navarra, S. A.,
A. C. 1311, 31080 Pamplona, Spain


Fine structure of the primary eyes in Heterochthonius gibbus (Oribatida, Heterochthoniidae) with some general remarks on photosensitive structures in oribatid and other actinotrichid mites.


Heterochthonius gibbus is an oribatid mite which has three eyes located on the prodorsum: an externally unpaired median eye, and a pair of posterolateral eyes. The fine structure of these eyes shows that they consist of a few retinula cells bearing rhabdomeric microvilli. The median eye has two small retinas that are inverted with respect to the cuticular cornea (lens) and each lateral eye has a single retina that is everted. In both types, a thin corneagen layer is located underneath the cornea. The receptor cells are partly surrounded by pigment cells, which are derived from epidermal cells. The location and structure of the eyes, representing typical arachnid ocelli, suggest that they are plesiomorphic structures in contrast to the clear spots and lenticuli occurring on the notogaster of some so called higher Oribatida (Brachypylina). A scenario which could describe the evolution of photosensitivity or photosensitive structures in oribatid mites is presented. Since clear spots and the spectacular lenticuli evidently are apomorphic features, their potential value for phylogenetic systematics is stressed.


evolution, lenticulus, naso, secondary eyes, ultrastructure