Each flattened hemilamella constitutes a narrow, hemolymph-filled space delimited by the flanges of two opposing layers of pillar cells, the bases of which adjoin in the mid-region of the lamella.
The present study thus examines the ultrastructure of the pillar cells, particularly their apical microvilli and junctions, in the gills of Macrobrachium olfersii, a strongly hyperosmore-gulating, freshwater palaemonid shrimp (McNamara, 1987).
The numerical density of the apical microvilli was also sampled in the same regions of the pillar cells. A second test system comprising a straight line 125 mm in length (equivalent to 5.0 [[micro]meter] at 25,000X) was placed over the micrograph at random, although parallel to the plane of the cuticle.
The present study focuses particularly on the ultrastructure of the flange and perikaryon regions of the pillar cells, which form the principal epithelial barrier between the hemolymph and the external medium.
The apical membrane of the pillar cells, overlain by the fine gill cuticle [249.0 [+ or -] 4.4 nm (n = 10) thickness], is folded into an extensive system of microvilli [ILLUSTRATION FOR FIGURE 4 OMITTED] that are organized into small tufts of from 4 to 8 villi [ILLUSTRATION FOR FIGURE 7 OMITTED].
The apical flange region of the pillar cells becomes attenuated and thinner as the distance from the perikaryon increases, attaining only 1.38 [+ or -] 0.30 [[micro]meter] (n = 6) in thickness at the extreme margins [ILLUSTRATION FOR FIGURE 9 OMITTED].
Typically, a single septal cell connects the bases of two adjacent pillar cells, its lateral ends interdigitating in a restricted manner with their basolateral membranes ([ILLUSTRATION FOR FIGURE 12 OMITTED], insert).
Various ultrastructural alterations appear in the pillar cells of the gill lamellae of M.
In the gill epithelium of Macrobrachium olfersii, the apical surface of the pillar cells is highly amplified by an extensive system of microvilli (type 2, see Cioffi, 1984).
olfersii attests to a dual role for the pillar cells in the regulatory physiology of the gill.
The notable reductions in the height and numerical density of the microvilli on the apical surface of the pillar cells, and in the thickness of the flanges, which occur as a result of acclimation to saline media in M.