2D2M:
reference: Structure of an extracellular giant hemoglobin of the gutless beard worm Oligobrachia mashikoi., Numoto N, Nakagawa T, Kita A, Sasayama Y, Fukumori Y, Miki K, Proc Natl Acad Sci U S A 2005 Oct 11;102(41):14521-6. Epub 2005 Oct 3. PMID: 16204001

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).