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ARTICLE

Microanatomical Characteristics of Marginal Ommatidia in Three Different Size-Classes of the Semi-Terrestrial Isopod Ligia exotica (Crustacea; Isopoda)

ESSI KESKINEN¹ , YASUHARU TAKAKU² , V. BENNO MEYER-ROCHOW³, TAKAHIKO HARIYAMA⁴

1 Department of Biology, University of Oulu, P.O. Box 3000, SF-90014 Oulu, Finland.
2 Department of Developmental Genetics, National Institute of Genetics, Mishima 411- 8540, Japan.
3 School of Engineering and Science, International University Bremen, D-28725 Bremen, Germany.
4 Department of Biology, Hamamatsu University School of Medicine, 1-20-1 Handayama, Hamamatsu, 431-3192, Japan

Corresponding Author: V.B. Meyer-Rochow, Fax: (+49 - 421) 200 49 3242. E-mail:

BIOCELL 2002, 26(3), 357-367. https://doi.org/10.32604/biocell.2002.26.357

Abstract

The aims of this paper have been (a) to characterize marginal ommatidia from different eye regions through a detailed description of their distinct ultrastructural features in three different size-classes of L. exotica, and (b) to compare microanatomical characteristics of the marginal ommatidia with those of ommatidia of the same eye, but located further centrally. On the basis of transverse as well as longitudinal sections we conclude that new ommatidia are added from a crescentic dorso-anterio-ventral edge of the eye and that maturing ommatidia go through a sequence in which originally the nuclei of cone -, pigment-, and retinula cells are arranged in three separate layers. At the beginning of the microvillar development, the organization of the corresponding rhabdomeres is still quite different (much less regular) from that of those rhabdomeres that make up the mature rhabdom. Marginal ommatidia always possess smaller diameters than more centrally located ones and retinal screening pigment granules are most apparent in the retinula cells only after the first microvilli have appeared. The diameters of rhabdom microvilli (approx. 55 nm) do not differ in ommatidia from the five investigated eye regions in small specimens (< 1.5 cm body length), but show a tendency to be slightly wider in the anterior (=frontal or rostral) regions of the eye (approx. 65 nm) in larger specimens (> 2.0 cm body length).

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