Rostrals and mentals of sea snakes of the genus Hydrophis in the Persian Gulf and Gulf of Oman: a tip of rostral decurved, pointed and beaked shaped, mental narrow, elongate and dagger-shaped (Hydrophis schistosus) b and c tip of rostral markedly tridentate, mental short and triangulate (H. viperinus and H. curtus, respectively) d tip of rostral markedly unidentate, mental short and triangulate (H. ornatus) e–h tip of rostral slightly unidentate, mental short and triangulate (H. ornatus, H. spiralis, H. cyanocinctus and H. platurus, respectively).