Degrees of vacuolation of the absorptive intestinal cells of five Sagitta (Chaetognatha) species: possible ecophysiological implications |
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Authors: | Y Perez J-P Casanova J Mazza |
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Institution: | (1) UPRES Biodiversité, Laboratoire de Biologie Animale (Plancton), Case 18, Université de Provence, 3, Place Victor Hugo, 13331 Marseille Cedex 3, France Fax: +33-4-91106333; e-mail: bioplank@newsup.univ-mrs.fr, FR |
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Abstract: | The cell organization and ultrastructure of the intestine have been studied in five species of Sagitta, one epiplanktonic (S. bipunctata Quoy and Gaimard, 1827), four mesoplanktonic (S. megalophthalma Dallot and Ducret, 1969, S. decipiens Fowler, 1905, S. minima Grassi, 1881, S. zetesios Fowler, 1905). The intestinal epithelium is composed of two ciliated cell types. The first (S-cell) principally occurs in
the anterior intestine and represents typical secretory cells. The second (A-cell) occurs in the median and posterior intestine
and displays ultrastructural features involved in absorption and intracellular digestion, that is, coated pits, endocytotic
vesicles, cytoplasmic tubules, and two distinct types of digestive vacuoles. Whereas S-cells exhibit few ultrastructural differences
among the five species, the vacuolar volume of the A-cells located in the mid portion of the intestine is higher in the mesoplanktonic
species. In S. zetesios and S. megalophthalma, each side of the median intestine comprises several hypervacuolated A-cells visible in transverse section; their degree
of vacuolation is inversely proportional to their number. The increased volume of the intestinal vacuoles is most marked in
S. decipiens and S. minima; in both these species, each lateral side of the median intestine displays a single ultravacuolated A-cell. The possible
ecophysiological implications of intestinal vacuoles are discussed in relation to patterns of the vertical distribution of
several Sagitta species. The vacuoles are presumed to regulate buoyancy, enabling the mesoplanktonic species to make vertical diel migrations.
Received: 22 January 2000 / Accepted: 28 July 2000 |
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