Dense granule-containing cells in the wall of the branchio-cardiac veins of a fresh water crayfish (Astacus leptodactylus).

The anatomical structure of oxygen-sensitive receptors in branchio-cardiac veins of a crayfish (Astacus leptodactylus) was studied with fluorescence and electron microscopy. Fluorescent cells were observed in the wall of a restricted part of the branchio-cardiac veins which was electrophysiologically shown to be a chemoreceptor region. Electron microscopy disclosed that they were dense granule-containing cells, and form, together with supporting cells and nerve terminals, complex structures that show gross similarities with arterial chemoreceptor structures in vertebrates.