Premium
Comparative aspects of the fine structure of the eyes of Phalangida (Arachnida) and certain correlations with habitat *
Author(s) -
Curtis D. J.
Publication year - 1970
Publication title -
journal of zoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0952-8369
DOI - 10.1111/j.1469-7998.1970.tb02904.x
Subject(s) - retina , biology , endoplasmic reticulum , vesicle , lens (geology) , retinal , membrane , biophysics , ultrastructure , anatomy , microbiology and biotechnology , biochemistry , neuroscience , paleontology
The eyes of seven species of Phalangida (Arachnida) were studied using electron microscope techniques. A fairly typical uni‐lenticular ocellus, the phalangid eye has beneath the lens a glassy body of lentigen cells, which are separated from the retina by a pre‐retinal membrane. The retina consists of hexagonally packed cylindrical retinulae, directed towards the dioptric apparatus. Each retinula comprises four cells, each of which contributes to the central cylindrical rhabdom by means of microvillar foldings of their plasma membranes. The only other cells in the retina constitute the glial system, with their somas situated proximally and with long cylindrical processes, each characterized by a central microtubule, passing distally in the interstices between the retinulae. Although there are none in the retina, laterally sited pigment cells prevent stray light entry, aided by cuticular pigmentation and hypodermal cell inclusions. The eyes of the various species show similarities correlated with their common function: sublenticular membrane modifications, many pigment granules separating the rhabdoms, many well‐developed mitochondria in the photoreceptor cells and many rhabdomal microvilli providing a large membrane surface area for photoreception. Distal rhabdom fusion could possibly serve either to transmit excitation between rhabdoms (providing increase in sensitivity) or, less likely, inhibition (providing increase in acuity). Peri‐rhabdomeric vesicles in all the species are functionally significant. Some interspecific differences may be considered to have a purely physiological basis, such as the relative abundance of rough endoplasmic reticulum in the lentigen cells, the condition of the pre‐retinal membrane, variations in microvillar diameters etc. Other differences, such as the relative height of the lentigen cells, may be correlated with ecological factors. The extreme differences in the eyes of Nemastoma lugubre (very short lentigen cells, disorganized rhabdoms, cellular sheath behind eye) possibly indicated some degree of regression, correlated with the animal's environment.