ommatidium

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ommatidium

(ŏm′ə-tĭd′ē-əm)
n. pl. ommatid·ia (-ē-ə)
One of the optical units, consisting of photoreceptors and usually one or more lenses, that make up a compound eye of an insect or a crustacean.

om′ma·tid′i·al (-ē-əl) adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

ommatidium

(pl. ommatidia) any of the numerous facets which make up the compound eye of insects and other arthropods. Each ommatidium has its own lens and is composed of a group of retinal cells surrounded by pigment cells. The light-sensitive part of the ommatidium is the RHABDOM, and on its receiving a stimulus a photochemical reaction takes place which results in impulses being sent to the optic nerve.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

ommatidium 

One of the visual elements of the compound eye of arthropods. It is hexagonal in shape and about ten times longer than its diameter. It consists of a corneal facet below which is a crystalline cone which collects light and a sensory area called the rhabdom, all of it being enclosed in a dark pigment.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann
References in periodicals archive ?
boggessi embryos have large head lobes and show ommatidial differentiation during the third post-naupliar stage (Fig.
All individuals of Ligia exotica examined, irrespective of size, possessed apposition-type compound eyes with a hexagonal ommatidial lattice.
exotica, because rhabdomeres are frequently skewed and the axes of ommatidial groups of retinula cells are not always parallel to the axes of the dioptric structures.
We observed a gradient of ommatidial diameters within the array, with the largest ommatidium at the posterior apex, and the smallest at the base.
Curiously, the ventral scars moved dorsally by about 5 ommatidial diameters.
3), each of which normally appears in two of the six ommatidial rows of the midband.
As a result, any incident rays at angles up to 12.5 [degrees] from the ommatidial axis will be retained within the rhabdom, assuming that the refractive indices of the rhabdoms and the surrounding retinular cells are similar to those of other decapods (e.g., Gaten, 1994).
When related to overall ommatidial length, the dioptric apparatus in the eye of Paralomis (though greatly enlarged in diameter) occupied significantly less space than the equivalent structure in the eye of the shallow-water Petrolisthes.
The differences in discharge patterns to single ommatidial and whole eye stimulation result from lateral inhibition in the retina, whereas the differences in slow potentials are a consequence of synaptic interactions in the lamina.