abnormal cell morphology abnormal endoplasmic reticulum morphology MP:0009378 MPheno.ontology The endoplasmic reticulum membranes form a complex meshwork of tubular channels, which are often expanded into slitlike cavities called cisternae. The ER takes two forms, rough (or granular), with ribosomes adhering to the outer surface, and smooth (with no ribosomes attached). abnormal ER morphology any structural anomaly of irregular network of unit membranes, visible only by electron microscopy, that occurs in the cytoplasm of many eukaryotic cells