The Hedgehog signaling pathway is one of the key regulators of animal development and is present in all bilaterians. The pathway takes its name from its polypeptide ligand, an intracellular signaling molecule called Hedgehog ("Hh") found in fruit flies of the genus "Drosophila"; fruit fly larva lacking the "Hh" gene are said to resemble hedgehogs. "Hh" is one of Drosophila's segment polarity gene products, involved in establishing the basis of the fly body plan. Larvae without "Hh" are short and spiny, resembling the hedgehog animal. The molecule remains important during later stages of embryogenesis and metamorphosis.