Mantis shrimps

Scientific name : Stomatopoda

The order Stomatopoda, belonging to crustaceans, includes not many species (about 400) in all the world. They are benthic animals, many are cryptic and not easy to observe. The largest species are very interesting, with some unique adaptations.
The front part of a mantis shrimp is covered by a short carapace (1) with part of the thorax and the abdomen (2) articulated and very mobile. The small head has typical compound eyes (3) -see description further on- and antennae (4) (sense organs). The main antennae are long and with 3 branches, also a flat antennal scale can be prominent in some species. Three pairs of walking legs (5) and a series of fin like appendages (pleopods) (6), are always moving. The last abdomen segment, or telson (7), has often bright colours ( warning colour), shown to intimidate the opponent.
Among the thoracic legs, a pair of very powerful raptorial legs (for prey capture) is prominent, somehow symilar to the praying mantis legs (8). Differences are: the impressive speed of the strike (the complete extension takes 3 milliseconds), and that stomatopods strike underhand (hitting the victim from below, where fish and crustaceans are often vulnerable).
Based on the raptorial legs shape, the mantis shrimps are classified into smashers and spearers: the former have a hardened, calcified heel on the outer edge of their raptorial appendage that they use to hammer hard-bodied prey like gastropods, crabs, and other crustaceans. Spearers have a formidable row of recurved spines on their raptorial appendage that are used to impale soft-bodied prey such as fish and shrimp. The power of the claw strike from a smasher has been has been likened to that of a bullet from a small caliber gun. It can, for example, break an aquarium glass. Some species, if teased, can react with terrible consequences (small bones ruptured). Mantis shrimps are benthic, many of the more colourful species live in quiet shallow environments (bay, lagoon, back reef). They are fish, crustaceans or mollusks predators.
Many species can dig U shaped burrows. In the spearer species, the male is the one coming out from the burrow to catch the preys, that consequently shares with the female. The latter spend most of the time in its shelter, concentrated on eggs production.
Eggs are guarded by the female until they hatch, from the eggs planktonic larvae are generated. Confusion is possible with shrimps. Usually the mantis shrimps have longer abdomen (tail), raptorial legs folded on the chest and different from the pince shaped shrimps' claws. The eye is unique (see below). The stomatopod's eye is divided in 2 emispheres by an equatorial belt, more or less wide. It is a compound eye, like in all crustaceans, made up by many (up to 10,000) cylindrical units, each one is a functionning eye (ommatidia). The shape of the eye allows 180° vision, even if the maximum sharpness is in the central part. The edge ommatidia are useful to perceive movements.
The eye divided in 2 parts (3 if we consider the belt) gives to the animal 2 (3) areas of maximum sharpness in a single eye: an eye alone has a stereoscopic vision. With 2 eyes those animals reach a tetraocular vision (from 4 points symultaneously), and an extraordinary capability to evaluate distances and to cohordinate very fast movements during the attack.
The spearer in particular have cylindrical eyes, even more effective in distances evaluation.
Often in the videos or photos black spots can be seen, moving quickly. This is called pseudopupil: the ommatidia that are looking toward the observer (lens), hit by lateral light, look black while the others, reflecting the light, are normally coloured.