Vol. 46 No. 2, 2007

Effects of Hypo- and Hypersaline Seawater on the Microanatomy and Ultrastructure of Epithelial Tissues of Echinometra lucunter (Echinodermata: Echinoidea) of Intertidal and Subtidal Populations

Ivonete A. Santos-Gouvea and Carolina A. Freire*

Departamento de Fisiologia, Setor de Ciências Biológicas, Universidade Federal do Paraná, Centro Politécnico, Curitiba, Paraná, 81531-990 Brazil

Ivonete A. Santos-Gouvea and Carolina A. Freire (2007) Echinoderms are widely distributed in intertidal zones and are thus subject to wide salinity variations and even air exposure. Physiological studies have shown them to be osmoconformers, but also to specifically, although moderately, regulate certain ions. Morphological studies associated with salinity challenges were not found in a literature search. Two populations of the sea urchin, Echinometra lucunter Linnaeus 1758, were studied: 1 intertidal and 1 subtidal population. Urchins from both populations were exposed for 5 d to hyposaline seawater (SW) of 25 ppt, or for 40 h to hypersaline SW of 45 ppt, and were compared to control urchins kept in full-strength SW of 35 ppt. Two external tissues, bathed by SW, the peristomial gills (PG) and ambulacral feet (AF), and 2 internal tissues, the coelomic wall of the ambulacral system (CWAS) and the intestinal rectum (IR), were investigated using transmission electron microscopy. With respect to the effect of salinity, there was more tissue damage in 45 ppt than in 25 ppt, coherent with the more-frequent SW dilution than concentration in marine shore habitats. Damage detected by electron microscopy included tissue disruption, destruction of microvillae, or evidence of fragmenting or peeling off of cells. Tissues of subtidal urchins were as sensitive to salinity stress as were those of intertidal urchins. PG, AF, and the IR presented evidence of an excretory function by the presence of large morula cells within these tissues. Only the IR displayed an ultrastructure compatible with metabolically active epithelia, in that it possessed numerous mitochondria.

Key words: Ambulacral feet, Hypersaline seawater, Intestinal rectum, Peristomial gills, Water vascular system.

*Correspondence: Tel: 55-41-33611712. Fax: 55-41-32662042. E-mail:cafreire@ufpr.br