Omega-shaped (as in the Greek capital letter) intracellular membrane-bounded organelle enriched in phosphatidylinositol 3-phosphate and dynamically connected to the endoplasmic reticulum. Omegasomes are the first step of the formation of autophagosomes via the phagophore assembly sites. [ http://www.ncbi.nlm.nih.gov/pubmed/24591649 http://www.ncbi.nlm.nih.gov/pubmed/18725538 ]