What is the X in X-mas?
(Prionace glauca), abundant shark of the family Carcharhinidae found in all oceans, from warm temperate to tropical waters. Also known as the blue whaler, the blue shark is noted for its attractive, deep-blue colouring contrasting with a pure-white belly. It is a slim shark, with a pointed snout, saw-edged teeth, and long, slim pectoral fins. Maximum length is about 4 metres (12 feet)