The membrane systems of the cardiac muscle cell of Meganychtiphanes norvegica (m. sars), euphauciacea, crustacea.

The membrane systems of cardiac muscle cells of the euphausiacean Meganychtiphanes norvegica are described. Transverse tubules are found both at the Z-band level (TZ-tubules) and at the H-band level (Th-tubules). Within the sarcomere narrow longitudinal tubules branch off from the TZ-tubules. At the H-band level these tubules expand forming flattened cisternae in dyadic and triadic couplings with the sarcoplasmic reticulum (SR). Adjacent myofibrils are separated by a well developed SR. Modifications of the SR are seen at the H-band level where junctional cisternae are formed.