ULTRASTRUCTURAL CHARACTERISTICS OF THE STRATIFIED SKIN EPITHELIUM OF AIDANOSAGITTA MACILENTA (CHAETOGNATHA) AND THEIR EVOLUTIOARY SIGNIFICANCE

Abstract

Objective - a detailed study of the ultrastructural characteristics of the stratified skin epithelium of Aidanosagitta macilenta - representative of phylum Chaetognatha which is considered as an ancient, early diverging branch of Bilateria. Materials and methods. Aidanosagitta macilenta Kassatkina (Chaetognatha, fam. Sagittidae) was investigated by transmission electron microscopy. The material was collected in summer (June-August) in the Peter the Great Gulf (Sea of Japan). The animals were fixed for 40-60 min at 4 ºС in cacodylate buffered 2,5 % glutaraldehyde (pH 7,4) and post-fixed in 2 % OsO4. The fixed material was dehydrated and embedded in Araldite. The ultrathin sections were examined with JEM-7 and JEM-100B electron microscopes. Results. The data obtained show unique epithelium structural characteristics: fibrillar structure of cell cytoplasm, special bridge-like intercellular junctions which have no analogues among the known types of intercellular junctions, primitive myelinization of nerve fibers locatd inside the epithelium. Skin epithelium of Chaetognatha is a primitive two-component tissue system where epithelial cells are closely associated with the elements of nervous tissue. Conclusions. The presence of stratified skin epithelium, special bridge-like intercellular junctions and mitochondria with tubular cristae is the evidence of Chaetognatha separate position in the phylogenetic system. Stratified skin epithelium of Chaetognatha and epidermis of vertebrates are not identical in structure, they represent a case of tissue parallelism. It can be assumed that the hypothetical ancestors of Bilateria had integuments in which epithelial and neural elements were combined.

Keywords

Chaetognatha / epithelia / Chaetognatha / intercellular junctions / evolution

References

[1] Атаманова М. В. Ультраструктурные особенности кожного эпителия Saccoglossus mereschkowskii (Enteropneusta) // Цитология. 1978. Т. XX, № 12. С. 1355-1359.

[2] Заварзин А. А. Сравнительная гистология. СПб.: Изд-во Санкт-Петербургск. ун-та, 2000. 518 с.

[3] Кусакин О. Г., Дроздов А. Л. Филема органического мира. Т. I. Пролегомены к построению филемы. СПб.: Наука, 1994. 282 с.

[4] Bromham L. D., Degnan B. M. Hemichordates and deuterostome evolution: robust molecular phylogenetic support for a hemichordate+echinoderm clade // Evol. Dev. 1999. Vol. 1, № 3. P. 166-171.

[5] Buryi G. I., Kasatkina A. P., Zhuravlev A. V., Safronov P. P. First finding of euconodont animals (Euconodontophylea) imprints on the territory of Russia // Zoosystematica Rossica. 2010. Vol. 19, № 1. P. 147-153.

[6] Cameron C. B., Garey J. R., Swalla B. J. Evolution of the chordate body plan: new insights from phylogenetic analyses of deuterostome phyla // Proc. Natl. Acad. Sci. USA. 2000. Vol. 97, № 9. P. 4469-4474.

[7] Duvert M., Bouligand Y., Salat C. The liquid cristalline nature of the cytoskeleton in epidermal cells of the chaetognath Sagitta setosa // Tissue Cell. 1984. Vol. 16. P. 469-481.

[8] Holland R. W., Garcia-Fernàndez J. Hox genes, developmental evolution and the origin of vertebrates // Ontogenez. 1996. Vol. 27, № 4. P. 273-279.

[9] Marlétaz F., Gilles A., Caubit X., Perez Y., Dossat C., Samain S., Gyapay G., Wincker P., Le Parco Y. Chaetognath transcriptome reveals ancestral and unique features among bilaterians // Genom Biology. 2008. 9: R94. doi: 10.1186/gb2008-9-6-r9

[10] Matus D. Q., Halanych K. M., Martindale M. Q. The Hox gene complement of a pelagic chaetognath, Flaccisagitta inflate // Integr. Comp. Biol. 2007. Vol. 47, № 6. P. 854-864.

[11] Ruddle F. H., Bentley K. L., Murtha M. T., Risch N. Gene loss and gain in the evolution of the vertebrates // Dev. Suppl. 1994. P. 155-161.

[12] Ruiz-Trillo I., Roger A. J., Burger G., Gray M. W., Lang B. F. A phylogenetic investigation into the origin of Metazoa // Mol. Biol. Evol. 2008. Vol. 25, № 4. P. 664-672.

[13] Telford M. J., Holland P. W. H. The Phylogenetic Affinities of the Chaetognaths: A Molecular Analysis // Mol. Biol. Evol. 1993. Vol. 10, № 3. P. 660-676.

[14] Turbeville J. M., Schultz J. R., Raff R. A. Deuterostome phylogeny and the sister group of the chordates: evidence from molecules and morphology // Mol. Biol. Evol. 1994. Vol. 11, № 4. P. 648-655.

[15] Shinn G. L. Chaetognatha // Microscopic Anatomy of Invertebrates. New-York: Wiley-Liss, 1997. Vol. 15. P. 103-220.

RIGHTS & PERMISSIONS

Stolyarova M.V., Kassatkina A.P.