The correct formation of blood vessels is essential for the development of a functional vasculature. Various mechanisms of vascular lumen formation have been described to date but, now, Wiebke Herzog and colleagues examine the development of common cardinal veins (CCVs) in zebrafish and show that these form via a previously undescribed mode of lumen formation (p. 2776). The researchers use in vivo time-lapse studies together with lineage tracing approaches to show that the angioblasts that form CCVs are specified as a population that is distinct from arterial-fated angioblasts. Once specified, these then form CCVs by a novel mechanism, which the authors term ‘lumen ensheathment’: endothelial cells (ECs) delaminate and align along an existing luminal space, extend via migration and eventually enclose the lumen. The delamination and migration events, they report, require cadherin 5, while EC proliferation within developing CCVs requires erythrocyte-derived Vegfc. These findings uncover a new mode of vessel formation, as well as highlighting important crosstalk between the haematopoietic and EC lineages.