Receptor for apelin receptor early endogenous ligand (apela) and apelin (apln) hormones coupled to G proteins that inhibit adenylate cyclase activity (PubMed:17412318, PubMed:16750822, PubMed:16876154). Plays a key role in early development such as gastrulation, blood vessels formation and heart morphogenesis by acting as a receptor for apela hormone, promoting endoderm and mesendoderm cell migration and regulating the migration of cells fated to become myocardial progenitors, respectively (By similarity). Promotes angioblast migration toward the embryonic midline, i.e. the position of the future vessel formation, during vasculogenesis (By similarity). May promote sinus venosus (SV)-derived endothelial cells migration into the developing heart to promote coronary blood vessel development (By similarity). Required for cardiovascular development, particularly for intersomitic vein angiogenesis by acting as a receptor for apln hormone (PubMed:17412318, PubMed:16750822, PubMed:16876154). Also plays a role in various processes in adults such as regulation of blood vessel formation, blood pressure, heart contractility, and heart failure (By similarity). Acts upstream of the i/o type of G-alpha proteins in the differentiation of endothelium, erythroid cells, myeloid cells and cardiomyocytes (PubMed:16876154). Internalized to the cytoplasm after exposure to apelin (apln) (PubMed:17412318). After exposure to apelin receptor early endogenous ligand (apela), internalized from the cell surface into an endosomal recycling compartment, from where it is recycled to the cell membrane (By similarity). Expressed in all blood vessels including the posterior cardinal vein, intersomitic veins and the vitelline vein network. At the gastrula stage, exclusively expressed in the mesodermal layer and at the neurula stage in the lateral plate mesoderm. Larval expression is observed in the endothelium of the primary blood vessels and the forming heart. Expression starts in the late blastula (stage 8), increases during gastrulation and remains constant between neurula and larva stages. Belongs to the G-protein coupled receptor 1 family. Truncated C-terminus.