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These benthic marine crustaceans can be up to 30cm long and spend most of their time in burrows [Wikipedia, 2012]. They are hunters and may be best known for their mode of attack. They have very powerful forward appendages which are used either for impaling or smashing prey or adversaries, and the forelimb strike of some mantis shrimp has been clocked at 14-23m/s for the striking surface. [Patek et al, 2004] The particular mode of destruction is a convenient grouping character and mantis shrimp species are commonly divided into “smashers” and “spearers” [Caldwell, web]
Mantis shrimp are highly visual animals and have extremely sophisticated eyes. Each eye is divided into three sections, an upper and lower lobe which detect light and movement, and a narrow band in between of color and polarization sensors. The upper and lower lobes can perceive the same visual space independently and hence provide depth perception within a single eye. (In some species, the eyes are dorsoventrally elongated, which further separates the viewpoints of the lobes.) This frees up the eyes to move independently of one another and scan opposite hemispheres if needed. The seemingly random eye movements also contribute to the monocular depth perception by allowing additional points of view on that eye’s visual space. The eye movements also distribute the color and polarization perception from the narrow central band across the visual field, or concentrate it on an object of interest, as needed. Mantis shrimps can see in up to twelve color bands, often extending into the ultra-violet [Marshall and Oberwinkler, 1999]. They can also perceive both linear and circular light polarization [Kleinlogel and White, 2008].
Why such an investment in vision? For one thing, most mantis shrimp tend to inhabit shallow, brightly lit tropical waters with abundant visual information. Many, in coral reef habitats, for instance, are surrounded by color information; these shallow dwelling species are more likely to have a wide spectrum of color perception and are more likely to see UV light than their deeper-water kin, who tend to have narrower spectral perception ranges commensurate with the available light spectrum. Much of this light is also partially polarized, by scattering, reflection off the air-water interface, and reflection off of biological surfaces, or refraction through transparent organisms [Cronin and Shashar, 2001].
In addition to their surroundings, predators and prey, mantis shrimp receive visual signals from each other. Fights between individuals are generally preceded by extensive posturing involving the antennae and mouthparts, during which the opponents watch one another closely [Dingle and Caldwell, 1969]. Courtship sometimes also involves an extended ritual during which females examine potential mates visually [Christy and Salmon, 1991]. Both of these are instances of trying to avoid violence. In the case of a fight, one of the combatants will often retreat before blows are exchanged, in response only to the posturing of the opponent.
In the case of courtship, the ritual often occurs when a male has visited a female at her burrow. Burrows are very important to mantis shrimp for protection from predators. During periods when females are receptive, individuals leave their burrows more often than usual to search for mates, and mortality is measurably higher. Mating success has value, but so does a good burrow, and fights between mantis shrimp are often over ownership of a burrow, even between males and females at the height of a mating cycle. So, a receptive female must first determine whether the male at her doorstep intends to mate with her or evict her and claim her burrow as his own. A visual inspection of his behavior may decide whether she emerges from the safety of her burrow entrance. His size may also be a factor. In some species, females mate only with smaller males, probably because the risk of eviction is less if the suitor is likely to lose in case of a fight [Christy and Salmon, 1991].
The duration of the pair bond varies considerably among species of mantis shrimp. In some species, visiting males never enter the female’s burrow, and leave immediately after mating. Depending on the length of the receptive period and how synchronized the females are, there may still be only one mating opportunity for most individuals, but in some species, females practice sperm storage and may mate at their convenience, perhaps many times before extruding and fertilizing their eggs. In other species, males stay in the burrow with their mates, guarding them from other males, until the eggs are extruded [Christy and Salmon, 1991]. In the family Lysiosquillidae, mated pairs appear to be monogamous and may stay together for six months or longer. Males do most of the hunting, and show anatomical differences that may be related to this: their eyes and forelimbs are larger than those of females. Although females spend more time in the burrow, males in the lab have been seen participating in the care of eggs [Caldwell, 2001]. Sharing of parental care in this manner is vanishingly rare in crustaceans.