Definition: "A cell type that produces platelets and coagulating factors that react to bleeding from blood vessel injury by clumping, thereby initiating a blood clot; and that, in embryos, emerge from the ventral mesoderm, just anterior to the ventral blood island. Embryonic thrombocytes are identified by cd41/itga2b.1 gene expression. Additional waves of emergence during development may occur but have not yet been described."