Ommatidium

Ommatidia (of spätgriech. Ommatidion = " little eyes " ) are the single eyes, from which the compound eyes of arthropods, including insects and crustaceans, are composed. Depending on the type, there is a compound eye only individual to many thousands of ommatidia, at the dragonflies, for example, up to 28,000 individual eyes.

An ommatidium is formed from five to nine ( in the Mandibulata always eight) sensory cells ( in the figure F), indoor show their microvilli ( rhabdomeres ) to the axis and form the rhabdome (E). The adjacent outwardly supporting and pigment cells separate the individual ommatidia from each other. The outer part of a dioptric Ommatidiums apparatus that is formed of a transparent high refractive Cornealinse (A) adjacent to the lower crystal cell or a crystal disc ( B). On the underside of the individual 's eye, the electrical pulses over a nerve axon of a nerve cell to the brain to be forwarded.

The formation of the cornea is carried out by said cells as a major pigment in crustaceans and insects as Corneagenzellen cells adjacent to the ommatidia. The Mandibulata also an educated originally from 4 crystal cone cells for further refraction of light is formed. Is the crystal cone created within the cells, it will be referred to as eukon, wherein the crystal system cone outside the cells is referred to pseudokon. Ommatidia without crystal cone within the insects are akon and in some species of beetle with a pin-like extension of the cornea, which takes over the crystal cone function, ommatidia are called exokon.

Phylogeny

The ommatidia and related to the compound eyes are regarded as Stammartmerkmal for the original Euarthropoda. They are found in both the extinct trilobites, as well as the recent insects, myriapods and crustaceans. In the arachnids, centipedes and millipedes to the compound eyes are resolved to single eyes, and corresponding in structure modified ommatidia. The belonging to the centipedes spiders runners ( andScutigera ) it came to so-called pseudo compound eyes to a renewed fusion of these Einzelommatidien.

Documents

  • Hannes Paul Euarthropoda, Arthropod ieS In: West Heath, Rieger (eds.): Systematic Zoology Part 1: protozoa and invertebrates. Gustav Fischer Verlag, Stuttgart, Jena, 1997. ISBN 3-437-20515-3
  • Herder Dictionary of Biology. Spektrum Akademischer Verlag GmbH, Heidelberg, 2003. ISBN 3-8274-0354-5
  • Entomology
  • Anatomy (eddy lots)
Odonata Photoreceptor cell Myriapoda
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