Observations on the morphology and histochemistry of the foregut muscles of spiders (Arachnida: Araneida)

The morphology of the foregut muscles of 5 spider families (Theraphosidae, Agelenidae, Araneidae, Lycosidae, Salticidae) was described, and the individual fiber numbers and fiber cross diameters of the muscles were determined. The nomenclature of these muscles was reviewed and modified if necessary. Oxidative enzyme and myosin-ATPase histochemistry revealed 8 dilatatory muscles of the foregut to consist of slow (type I) fibers, fast fibers (type IIB) and intermediate fibers, were only found in the 2 other muscles of the foregut, and in the remaining prosomal muscles (type IIA fibers around the poison gland). The 8 sucking muscles proper of the foregut also showed stronger activities of transmitter metabolizing enzymes [monoamine oxidase, glutamate dehydrogenase (NAD)], and comparatively distinct amounts of glycogen and lipids.