muscle cell morphology trait sarcoplasmic reticulum morphology trait Trait.ontology Any measurable or observable characteristic related to the shape, structure, color, or pattern of the endoplasmic reticulum of skeletal or cardiac muscle, i.e., the complex of vesicles, tubules, and cisternae that form a continuous structure around striated myofibrils, with a repetition of structure within each sarcomere. VT:0004088