endoplasmic reticulum rough endoplasmic reticulum Planarian_Anatomy PMID:30143032 Network of interconnected, flattened, and/or tubular membrane, known as cisternae. This membrane is contiguous with the outer nuclear membrane. The endoplasmic reticulum is involved in both protein and lipid synthesis. The outer surface is studded with protein-synthesizing particles known as ribosomes. https://orcid.org/0000-0003-2569-1939 | https://orcid.org/0000-0002-7535-4407 GO:0005791