title: Architecture of the T-system in helical paramyosin muscles of an annelid (Branchiobdella).
abstract: Tannic acid impregnation has revealed the existence of a T-system in the helical fibers of Branchiobdella pentodonta (Annelida, Clitellata). T-tubules are L-shaped inside the fiber, within the plane of the I-band: after a short horizontal tract they run longitudinally for a long tract keeping contact with many sarcoplasmic reticulum cisternae and forming dyads. The presence of a T-system in this annelid, the only one demonstrated up to now in annelids, is to be ascribed to the thickness of the contractile layer of those fibers.
mesh_terms: D000845:Annelida / Q000648:ultrastructure*; D003593:Cytoplasm / Q000648:ultrastructure; D049711:History, Modern 1601-; D008854:Microscopy, Electron; D009132:Muscles / Q000648:ultrastructure; D012508:Sarcolemma / Q000648:ultrastructure; D012519:Sarcoplasmic Reticulum / Q000648:ultrastructure*