Ornate

The body of the foot is large (from 10 to 34 cm long) and is divided into the following sections (or tagma ): protocephalon , jaw - chest from fused three jaw and four thoracic segments, chest from four free segments and a strongly developed segmented abdomen. The first pair of pectoral legs is sensory, the second to fifth pairs are grasping, and the last three pairs are walking. On the 1st-5th pairs of chest legs there are gills. The grasping legs have an unusual feature: in them the last segment is sharp, serrated, similar to a blade and inserted into the longitudinal furrow of the penultimate segment, like a penknife. The first pair of grasping legs is the largest, they grab prey, and the remaining grasping legs hold it. In terms of the structure of their grasping legs, rotonogs are similar to mantis insects, which was the reason for their name.

The abdominal region is longer than the front of the body. The first five abdominal legs are bifurcate, leaf-shaped, with feathery setae. The functions of the anterior abdominal legs are very diverse. Thanks to their swings, the ornate swim. In addition, on all the anterior abdominal legs there are gills in the form of thin-walled, repeatedly branching appendages. The first two pairs of abdominal legs in males are transformed into a copulative apparatus . The last pair of abdominal legs flattened. Together with telson, they form a caudal fin. Development with metamorphosis.

Vision

Mantis crayfish have one of the most complex visual systems ever studied ^[2] . If humans have three types of color-sensitive cones in their eyes, then mantis crayfish have 16. Moreover, mantis crayfish can adjust the sensitivity of their long-wavelength vision to adapt to the environment ^[3] . This phenomenon, known as “spectral tuning,” is expressed differently in different species ^[4] . Cheroske and his colleagues found no spectral adjustment in Neogonodactylus oerstedii , a species living in the most evenly lit environment. In N. bredini , a species that lives in various media with a depth of 5 to 10 m (occasionally up to 20 m), spectral tuning is recorded, but its ability to change the length of the most sensed wave is not as pronounced as in N. wennerae , the species with the largest ecological and light diversity of habitats.

The middle strip of the eye consists of six rows of specialized ommatidia - rosettes of photosensitive cells. Four rows contain up to 16 different pigments: 12 of them are color sensitive, and the rest are used as color filters. The vision of mantis shrimps perceives both polarized light and multi-zone images ^[5] . Their eyes (fixed on independent movable stems) themselves are multicolored and are considered the most complex eyes of the animal world ^[6] .

Each facet eye has up to 10,000 adjacent ommatidia. The eye consists of 2 oblate hemispheres, separated by 6 parallel rows of specialized ommatidia, collectively called the “middle band”. Thus, the eye is divided into three regions. This allows mantis crabs to see objects in three different parts of the eye. In other words, each eye has trinocular vision and depth perception. The upper and lower hemispheres are mainly used to distinguish between shapes and movements, as are the eyes of many other crustaceans.

Rows 1-4 of the middle band specialize in color perception, from ultraviolet to longer waves. Their ultraviolet vision captures five different wavelengths in the far UV range. For this, two photoreceptors are used in combination with four different color filters ^{[7] [8]} . At the moment, there is no evidence of the ability of mantis crayfish to see infrared light ^[9] . The optical elements in these rows include 8 different classes of visual pigments, and the rhabdom (the region of the eye receiving light from one direction) is divided into three different pigment layers (tiers), each for its own wavelength. Three tiers in rows 2 and 3 are separated by color filters (inter-household filters), which can be attributed to 4 distinct classes, two classes in each row. The design resembles a sandwich: a tier, a color filter of one class, again a tier, a color filter of another class, and finally a tier again. These color filters allow mantis shrimps to see many colors. Without filters, pigments perceive only a small fraction of the color spectrum: approximately 490-550 nm ^[10] . Rows 5-6 are also divided into different tiers, but have only one class of visual pigment (ninth) and specialize in polarized light. They register different polarization planes. The tenth class of visual pigments is only in the upper and lower hemispheres of the eye.

The middle band covers only 5-10 degrees of the field of view, but, like most crustaceans, the eyes of mantis crayfish are fixed on the stems. The movements of the eyes of the mantis crayfish are unusually free along any axis - up to 70 degrees - thanks to 8 independent eye muscles, combined in 6 groups. With the help of this muscle, a mantis shrine examines the environment through the middle lane, collecting information about the shapes, silhouettes and terrain inaccessible to the upper and lower hemispheres of the eye. They can also keep track of moving objects using sharp, sweeping eye movements performed independently by both eyes. Due to the combination of these various techniques, including movement in one direction, the middle band can cover a significant part of the field of view.

In some species, there are at least 16 types of photoreceptors, divided into four classes (the perceived spectrum is also refined by color filters in the retina), 12 of which are intended for color analysis at various wavelengths (including six that are sensitive to ultraviolet ^{[7] [11]} ) and four for polarized light analysis. For comparison: most people have only four visual pigments, of which three distinguish colors, and ultraviolet light is blocked by the cornea. At the exit from the retina, visual information turns into many parallel data channels leading to the central nervous system, which significantly reduces the need for further processing ^[12] .

In at least two species, the ability to perceive the circular polarization of light has been detected ^{[13] [14]} . Some of their biological quarter-wave plates work more reliably across the entire visual spectrum than any modern artificial polarizers, and suggest that they can inspire a new type of optical media that is more efficient than the current generation of Blu-ray ^{[15] [16]} .

The species of mantis shrimp Gonodactylus smithii is the only known organism capable of perceiving the four linear and two circular polarization components necessary to obtain all four Stokes parameters that fully describe polarization. Therefore, they have optimal polarization vision ^{[14] [17]} .

A huge variety of mantis shrimp photoreceptors was most likely due to gene duplication sometime in the past ^{[18] [10]} . An interesting consequence of this duplication is the mismatch of the number of transcripts of opsins and physiologically represented photoreceptors ^[10] . One species can have 6 different opsin genes, but only one spectral type of photoreceptor is presented. Over time, mantis shrimps have lost their original phenotype, although some still have 16 different photoreceptors and 4 light filters. Species that live in different light environments experience selection pressure to preserve the diversity of photoreceptors and better preserve the original phenotype than species living in muddy water or leading predominantly nocturnal lifestyles ^{[10] [19]} .

Assumptions about the benefits of the visual system

The benefits of polarization sensitivity are not clear; however, other animals use polarized vision to transmit mating signals and covert communication that does not attract the attention of predators. This mechanism may provide an evolutionary advantage; it also requires only minor changes in the cells of the eye and can easily develop under the influence of selection.

The eyes of mantis crayfish can allow them to distinguish between different types of coral, prey (which is often transparent or translucent), or predators such as barracuda with iridescent scales. Or, the method of hunting mantis shrimps (consisting in an extremely sharp movement of claws) may require very accurate information about space, in particular, accurate perception of distance.

During mating rituals, mantis shrimps actively fluoresce, and the wavelength of this fluorescence coincides with the perceived wavelength of pigments in their eyes ^[20] . Females are fertile only in certain phases of the tidal cycle; therefore, the ability to distinguish the phase of the moon prevents unnecessary efforts. It can also give mantis shrimp information about the power of the tide, which is important for organisms living in shallow water.

According to some assumptions, the ability to see ultraviolet light makes it possible to notice prey that would otherwise be difficult to recognize against the background of a coral reef ^[11] .

Studies show that the final color perception of mantis crayfish is not very different from human. Their eyes are a mechanism that acts at the level of individual cones and helps the brain work. This system preprocesses visual information in the eye, and not in the brain; otherwise, it would take a larger brain and a lot of energy to process such a stream of solid data. Although their eyes are very complex and not yet fully understood, the principle of the system seems simple ^[21] . He is like a human eye, only acts the other way around. In the inferior temporal cortex of the human brain is a huge number of color-specialized neurons that process visual impulses from the eyes and create color images. Instead, mantis shrimps use different types of photoreceptors in the eyes, giving the same result as human color neurons. This is an innate and more effective system for an animal that needs to constantly analyze colors. Humans have fewer types of photoreceptors, but more color neurons, while mantis crayfish, apparently, have less color neurons, but more classes of photoreceptors ^[22] .

The vast majority of species lives in tropical and subtropical seas at shallow depths. Praying mantis crayfish are edible and are found in the Far Eastern seas off the Russian coast. In the Mediterranean Sea, Squilla mantis is common. In the Indian and Pacific Oceans, large-footed fisheries are being fished.

Most of the footed burrows in the sea soil. Small species of the genera Gonodactylus and Coronida are hidden in crevices and crevices between the branches of coral. Some smaller species use larger burrows.

Distributed in warm seas and lead a predatory lifestyle. Most of the time the rotopods spend in burrows. Climbing out, they crawl along the surface of the soil with the help of the hind pectoral legs, as well as the hunting jaws, which at the same time bend and on which the cancer rests, like crutches. Crayfish can swim quite quickly. Mantis crayfish burrow into the ground with the front end of the body, wielding rostrum and leg jaws. The finished hole usually has two exits, and the water, guided by the sweeps of the front abdominal legs, flows freely through it. The Lysiosquilla excavathrix burrows reach a depth of 1 meter.