Mantis shrimp, or stomatopods, are carnivorous marine crustaceans of the order Stomatopoda, branching from other members of the class Malacostraca around 340 million years ago. Mantis shrimps typically grow to around 10 cm (3.9 in) in length, while a few can reach up to 38 cm (15 in). A mantis shrimp's carapace covers only the rear part of the head and the first four segments of the thorax. Varieties range in colour from shades of brown to vivid colours, with more than 450 species of mantis shrimp being known. They are among the most important predators in many shallow, tropical and subtropical marine habitats. However, despite being common, they are poorly understood, as many species spend most of their lives tucked away in burrows and holes.