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A modification of the conventional method for the staining of ultrathin sections resulted in an increase in contrast of ultrastructural detail in tissues. Tissues embedded in Spurr's low viscosity embedding medium were stained with freshly centrifuged Reynolds' lead citrate for 1-5 min, rinsed in double distilled water and dried prior to staining with a saturated solution of uranyl acetate for 40 min, and freshly centrifuged Reynolds' lead citrate for 20 min.Sections treated by this procedure showed enhanced staining of cellular organelles and cytoplasmic matrix. This procedure is recommended for tissues with poor staining qualities resulting from either prolonged fixation or from inadequacies in the buffer or embedding medium used.

Pteriomorphian spermatozoa, like those of most other bivalves, are of the classic aquasperm type (conical acrosomal vesicle, short to rod-shaped nucleus, short midpiece composed of two centrioles and a ring of spherical mitochondria, a simple flagellum). Whereas most other bivalve subclasses show at least some defining acrosomal feature(s), this does not appear to be the case within the Pteriomorphia. While this could indicate non-monophyletic status, it also correlates with the fact that the Pteriomorphia are a very old and very successful group of bivalves. Acrosomal similarities suggest a close link between the Ostreoidea and Limoidea (acrosomal vesicle with wedge-shaped apical zone; radiating plates present but not well developed); and between the Pterioidea, Pinnoidea and Pectinoidea (dense anterior layer; very well developed radiating plates). For supposedly closely related taxa, the Arcoidea and Limopsoidea (both Arcoida) differ markedly from each other in acrosomal shape and substructure. The affinities of the Anomioidea and even more so the Mytiloida remain uncertain, the latter possibly connected with the Pterioidea or, more likely, removed from the rest of the Pteriomorphia (mytiloid acrosomes show concentric lamellae). A very close relationship between the Pectinidae and Spondylidae of the Pectinoidea is demonstrated (dense anterior layer of acrosome recurved). Within the Mytilidae (Mytiloidea) there is substantial variation in sperm morphology between supraspecific taxa especially at the subfamial level.

Two types of ampullary organs are present in the skin of the freshwater salmontail catfish, Arius graeffei, each consisting of a short canal (0.2-0.5 mm) oriented perpendicular to the basement membrane and ending in an ampulla. Histochemical staining techniques (Alcian blue and Lillie's allochrome) indicate that the ampullary canals contain an acidic mucopolysaccharide gel, which is uniform in its staining properties along the canals. Type II ampullary organs consist of a canal, the wall of which is lined with cuboidal epithelial cells. The canal opens into an ampulla with 50-60 receptor cells. Electron microscopy reveals that the pear-shaped receptor cells bear microvilli on their luminal surface and lie adjacent to an unmyelinated neuron. Type III ampullary organs differ from Type II in that the canal wall consists of cells that possess a protein-rich sac at the luminal apex and have a polymorphic nucleus. The canals of Type III ampullary organs open to an ampulla with 8-30 receptor cells similar in both staining properties and structure to those of the Type II organ. In both types of ampullary organs, supportive cells surround each receptor cell except at the apex of the receptor cell.