The Myocardial Ultrastructure of Hemilamprops rosea and Leucon nasica (Crustacea, Cumacea) and its Phylogenetic Implications

The heart wall of Hemilamprops rosea and Leucon nasica is innervated and consists of a single-layered epicardium and a single-layered myocardium. Their heart ultrastructure does not differ. Large lipid-containing cells are found in the heart lumen. The membrane systems conform to the typical eumalacostracan condition, with the isopods as the only exception. The transverse tubular system at the Z- and H-levels is connected by longitudinal tubules. The sarcoplasmic reticulum, which forms a fenestrated sheath around the myofibrils, is continuous across the Z-band and modified at the H-level only. The interior and peripheral couplings are located at the H-level. The posterior and anterior aorta lack contractile material. The aorta valves are bicuspid.