Springer Nature is making SARS-CoV-2 and COVID-19 research free. View research | View latest news | Sign up for updates

Fine structure and its functional properties of the endostyle of Ascidians,Ciona intestinalis

A part of phylogenetic studies of the thyroid gland

  • 94 Accesses

  • 21 Citations


For the purpose used in understanding thyroid phylogenesis, the fine structure and the iodine metabolism of the endostyle of Ascidians,Ciona intestinalis, was studied by electron microscopy and electron microscopic autoradiography. There are 8 kinds of zones in the endostyle.

Zone 1, 3, and 5 cells, especially zone 1 cells, are characterized by numerous long cilia. These cells which show no indications of protein-secretion but numerous small vesicles and cytoplasmic filaments might play a role in catching and transporting food, absorption of liquid and supporting the endostylar construction.

Zone 2, 4, and 6 cells are large and characterized by well developed rough endoplasmic reticulum and numerous electron-dense secretory granules which are considered to be synthesized in the rough endoplasmic reticulum and transported to the Golgi apparatus to mature. They, which are somewhat similar to the pancreatic exocrine cells in fine structure, are believed to secrete the proteinous or mucoproteinous substances which might be related to the digestion of food.

Zone 7 and 8 cells which might be homologous to the thyroid cell of the higher vertebrate contains poorly developed rough endoplasmic reticulum, small Golgi apparatus, a few multivesicular bodies, a few lysosomes, and numerous small vesicles. In addition zone 8 cells bear cilia on their apical surface. The cytoplasmic characteristics of these cell types, especially of zone 8 cells, are fairly similar to those of type 2C and type 3 cells of the endostyle of a larval lamprey, though the rough endoplasmic reticulum is not so well developed. By electron microscopic autoradiography numerous silver grains were observed on the apical cell membrane region of zone 7 and 8 cells, especially of zone 8 cells, 1, 4, 6, 16 and 24 hours after immersion in sea water containing125I. This fact suggests that the iodination takes place in the apical cell membrane region of these cells. The materials in the endostylar lumen is washed away during the fixation and dehydrating processes of the tissue. Therefore, the possibility of iodination of thyroglobulin-like substances taking place within the endostylar lumen cannot be ruled out. Grains were also found in the multivesicular bodies and lysosomes after 4, 6, 16 and 24 hours, especially 16 and 24 hours. It seems that the organic iodine might be reabsorbed into the cytoplasm of these cells.

This is a preview of subscription content, log in to check access.


  1. Bargmann, W.: Die Schilddrüse. In: Handbuch der mikroskopischen Anatomie des Menschen (W. v. Möllendorff, ed.), Bd. VI/2, S. 22–23. Berlin: Springer 1939.

  2. Barrington, E. J. W.: The distribution and significance of organically bound iodine in the ascidianCiona intestinalis. J. Mar. Biol. Ass. U.K.36, 1–16 (1957).

  3. —: Some endocrinological aspects of the protochordata. In: Comparative endocrinology, ed. by A. Gorbman. New York: Wiley 1959.

  4. —: Hormones and evolution. London: Einglish Univ. Press 1964.

  5. —: The biology of hemichordata and protochordata. Edinburgh: Oliver and Boyd 1965.

  6. —, Barron, N.: On the organic binding of iodine in the tunic ofCiona intestinalis. J. Mar. Biol. Ass. U.K.39, 513–525 (1960).

  7. —, Franchi, L. L.: Organic binding of iodine in the endostyle ofCiona intestinalis. Nature (Lond.)177, 432 (1956).

  8. —, Thorpe, A.: An autoradiographic study of the binding of iodine125I in the endostyle and pharynx of the ascidians,Ciona intestinalis L. Gen. comp. Endocr.5, 373–385 (1965).

  9. Covelli, I., Salvatore, G., Sena, L., Roche, J.: Sur la formation d'hormones thyroidiennes et de leurs précurseurs parBranchiostoma lanceolatum Pallas (Amphioxus). C. R. Soc. Biol. (Paris)154, 1165–1189 (1960).

  10. Dohrn, A.: Thyreoidea bei Petromyzon,Amphioxus und den Tunicaten. Mitt. Zool. stat. Napel6, 49–92 (1886).

  11. Egeberg, J.: Iodine-concentrating cells in the endostyle ofAmmocoetes. Z. Zellforsch.68, 102–115 (1965).

  12. Fujita, H.: Studies on the iodine metabolism of the thyroid gland as revealed by electron microscopic autoradiography of125I. Virchows Arch. Abt. B2, 265–279 (1969).

  13. - Outline of the fine structural aspects on the synthesis and release of the thyroid hormone. Gunma Symp. Endocrinol. (in press).

  14. —, Honma, Y.: Some observations on the fine structure of the endostyle of larval lampreys, ammocoetes ofLampetra japonica. Gen. comp. Endocr.11, 111–131 (1968).

  15. — —: Iodine metabolism of the endostyle of larval lampreys, ammocoetes ofLampetra japonica. Electron microscopic autoradiography of125I. Z. Zellforsch.98, 525–537 (1969).

  16. Hoheisel, G.: Untersuchungen zur funktionellen Morphologie des Endostyls und der Thyreoidea vom Bauchneunauge (Lampetra planeri Bloch.). I. Untersuchungen am Endostyl. Morph. Jb.114, 204–240 (1969).

  17. Ibrahim, M. S., Budd, G. C.: An electron microscopic study of the site of iodine binding in the rat thyroid gland. Exp. Cell Res.38, 50–56 (1965).

  18. Kennedy, G. R.: The distribution and nature of iodine compounds in ascidians. Gen. comp. Endocr.7, 500–511 (1966).

  19. Müller, W.: Über die Entwicklung der Schilddrüse. Jena. Z. Naturw. Med.6, 428–460 (1871).

  20. —: Über die Hypobranchialrinne der Tunicaten und deren Vorhandensein beiAmphioxus und den Cyclostomen. Jena. Z. Naturw.7, 327–332 (1873).

  21. Nadler, N. J.: Iodination of thyroglobulin in the thyroid follicle. In: Current topics in thyroid research. New York: Academic Press 1965.

  22. —, Young, B. A., Leblond, C. P., Mitmaker, B.: Elaboration of thyroglobulin in the thyroid follicle. Endocrinology74, 333–354 (1964).

  23. Olsson, R.: Endostyle and endostylar secretions. A comparative histochemical study. Acta zool. (Stockh.)44, 299–328 (1963).

  24. —: The cytology of the endostyle ofOikopleura dioica. Ann. N.Y. Acad. Sci.118, 1038–1051 (1965).

  25. Seljelid, R.: Endocytosis in thyroid follicle cells. IV. On the acid phosphatase activity in thyroid follicle cells, with special reference to the quantitative aspects. J. Ultrastruct. Res.18, 237–256 (1967).

  26. Stein, O., Gross, J.: Metabolism of I125 in the thyroid gland studied with electron microscopic autoradiography. Endocrinology75, 789–798 (1964).

  27. Tong, W., Kerkoff, P., Chaikoff, I.L.: Identification of labelled thyroxine and triiodothyronine in amphioxus treated with131I. Biochem. biophys. Acta (Amst.)56, 326–331 (1962).

  28. Welsch, U., Storch, V.: Zur Feinstruktur und Histochemie des Kiemendarmes und der Leber vonBranchiostoma lanceolatum (Pallas). Z. Zellforsch.102, 432–446 (1969).

  29. Wollman, S. H., Burstone, M. S.: Localization of esterase and acid phosphatase in granules and colloid droplets in rat thyroid epithelium. J. Cell Biol.21, 191–201 (1964).

Download references

Author information

Additional information

This investigation was supported by research grant from Dr. Henry C. Buswell Research Fellowship.

On leave from Department of Anatomy, Hiroshima University, School of Medicine, as a Visiting Research Professor. The authors wish to express their hearty thanks to Dr. Oliver P. Jones for his valuable criticism.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Fujita, H., Nanba, H. Fine structure and its functional properties of the endostyle of Ascidians,Ciona intestinalis . Z.Zellforsch 121, 455–469 (1971). https://doi.org/10.1007/BF00560154

Download citation


  • Endostyle
  • Ascidians
  • Zones
  • Iodination
  • Homology to the Thyroid