Ultrastructure of the crayfish kidney--coelomosac, labyrinth, nephridial canal.

Abstract

AbstractRegions of the crayfish kidney were examined by electron microscopy. Coelsmosac cells are loosely bound together by desmosome‐like spot junctions, and connected to the basal lamina via characteristic pedicels. The cytoplasm contains numerous vesicles and vacuoles of various sizes and is often crowded with large, lysosome‐like granules or dense bodies. The morphology suggests a filtration mechanism with reabsorption of materials such as protein from the filtrate and secretion of other substances into the lumen.The labyrinth is composed of cuboidal to columnar cells which possess a brush border, long and narrow intercellular spaces, basal plasmalemmal invaginations and typical cytoplasmic components. Two sub‐regions are distinguishable. The morphology of labyrinth I suggests that these cells move fluid isotonically across the epithelium. Labyrinth II, in addition to isotonic transport, appears to be more active in the endocytic uptake and intracellular digestion of large molecules such as protein.The nephridial canal consists of cells which lack a brush border, but display extensive basal invaginations associated with elongated mitochondria. A proximal and distal region are cytologically distinguishable. Proximally, the cells are small and filled with mitochondria throughout. Scattered within the cytoplasm are vesicles, vacuoles, diffuse glycogen, free ribosomes, dense bodies and some rough endoplasmic reticulum. Distally, the cells are less compact, larger, and cuboidal to columnar in shape. The cytoplasm is similar to that of the proximal cells, but the basal invaginations are even larger and more extensive. The morphology of cells in both regions of the nephridial canal is highly suggestive of active solute reabsorption, probably occurring against an osmotic gradient.