A part of the endomembrane system in the form of an invagination of a membrane upon which a clathrin coat forms, and that can be converted by vesicle budding into a clathrin-coated vesicle. Coated pits form on the plasma membrane, where they are involved in receptor-mediated selective transport of many proteins and other macromolecules across the cell membrane, in the trans-Golgi network, and on some endosomes. [ http://www.neurolex.org/wiki/sao1969557946 http://www.ncbi.nlm.nih.gov/pubmed/10559856 http://www.ncbi.nlm.nih.gov/pubmed/17284835 https://www.worldcat.org/search?q=bn%3A0198506732 ]