Ultrastructure of cardiac muscle of Trochosa terricola Thor., Pardosa amentata Clerck, P. pullata Clerck, and Pisaura mirabilis Clerck (Araneae: Lycosidae, Pisauridae).

The ultrastructure of the cardiac muscle in some araneae has been investigated. The sarcolemma invaginates at the Z band and may extend into the cells through several myofibrils. Numerous T-tubules are given off both from sarcolemmal invaginations and also directly from the cell surface. In passing through the Z band, the luminal diameter of T-tubules greatly increases. Dyadic and a few triadic couplings are found mainly at the A-I level. Peripheral couplings were not seen.