Mantis shrimp
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.[2] Mantis shrimp typically grow to around 10 cm (3.9 in) in length, while a few can reach up to 38 cm (15 in).[3] A mantis shrimp's carapace (the hard, thick shell that covers crustaceans and some other species) 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 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.[4]
Called "sea locusts" by ancient Assyrians, "prawn killers" in Australia,[5] and now sometimes referred to as "thumb splitters"—because of the animal's ability to inflict painful wounds if handled incautiously[6]—mantis shrimp have powerful raptorials that are used to attack and kill prey either by spearing, stunning, or dismembering. Some mantis shrimp species have specialised calcified "clubs" that can strike with great power, while others have sharp forelimbs used to seize the prey (hence the term "mantis" in its common name).
About 450 species of mantis shrimp have been discovered worldwide; all living species are in the suborder Unipeltata, which arose around 193 million years ago.[2][7]
These aggressive and typically solitary sea creatures spend most of their time hiding in rock formations or burrowing intricate passageways in the sea bed. They rarely exit their homes except to feed and relocate, and can be active during the day, nocturnal, or crepuscular (active at twilight), depending on the species. Unlike most crustaceans, they sometimes hunt, chase, and kill prey. Although some live in temperate seas, most species live in tropical and subtropical waters in the Indian and Pacific Oceans between eastern Africa and Hawaii.
Mantis shrimp live in burrows where they spend the majority of their time.[8] The two different categories of mantis shrimp—spearing and smashing—favour different locations for burrowing.[8] The spearing species build their habitat in soft sediments and the smashing species make burrows in hard substrata or coral cavities.[8] These two habitats are crucial for their ecology since they use burrows as sites for retreat and as locations for consuming their prey.[8] Burrows and coral cavities are also used as sites for mating and for keeping their eggs safe.[8] Stomatopod body size undergoes periodic growth which necessitates finding a new cavity or burrow that will fit the animal's new diameter.[8] Some spearing species can modify their pre-established habitat if the burrow is made of silt or mud, which can be expanded.[8]
The mantis shrimp's second pair of thoracic appendages has been highly adapted for powerful close-range combat. The appendage differences divide mantis shrimp into two main types: those that hunt by impaling their prey with spear-like structures and those that smash prey with a powerful blow from a heavily mineralised club-like appendage. A considerable amount of damage can be inflicted after impact with these robust, hammer-like claws. This club is further divided into three subregions: the impact region, the periodic region, and the striated region. Mantis shrimp are commonly separated into two distinct groups determined by the type of claws they possess:
