Mineral congregations, “spherites” in the midgut gland ofCoelotes terrestris (Araneae): Structure, composition and function

Summary Spherites in the digestive and secretory cells of the midgut gland of the agelenid spiderCoelotes terrestris were studied by electron microscopy and histochemical methods. Spherites measured 1–6 µm in diameter and were characterized by alternating layers of electron dense and electron lucent material. The main-components of spherites were calcium phosphates and calcium carbonates. Guanine and barium, as well as aminopeptidase and alkaline phosphatase were also present. The matrix consisted of proteins and carbohydrates. Numerous spherites were found together with excretory products within the excretory vacuoles of the digestive cells.