Қиғаш еңкеулер: морфологиясы, таралуы және экологиясы

Decapod crustaceans in the infraorder Anomura

Squat lobsters are dorsoventrally flattened crustaceans with long tails held curled beneath the cephalothorax. They are found in the two superfamilies Galatheoidea and Chirostyloidea, which form part of the decapod infraorder Anomura, alongside groups including the hermit crabs and mole crabs. They are distributed worldwide in the oceans, and occur from near the surface to deep sea hydrothermal vents, with one species occupying caves above sea level. More than 900 species have been described, in around 60 genera. Some species form dense aggregations, either on the sea floor or in the water column, and a small number are commercially fished.

The two main groups of squat lobsters share most features of their morphology. They resemble true lobsters in some ways, but are somewhat flattened dorsoventrally, and are typically smaller, ranging from 0.7 to 3.5 inches in length. Squat lobsters vary in postorbital carapace length (measured from the eye socket to the rear edge), from in the case of Munidopsis aries, down to only a few millimetres in the case of Galathea intermedia and some species of Uroptychus. The cephalothorax is made of 19 body segments (somites), although the divisions are not obvious and are most easily inferred from the paired appendages. From front to back, these are the two pairs of antennae, six pairs of mouthparts (mandibles, maxillae, maxillules and three pairs of maxillipeds), and five pairs of pereiopods. In Munida Sarsi, the farther the mouthparts are located from the mouth, the more complex in movement and functional scheme they are. The trend of larger numbers of eggs and smaller sized eggs is mostly found in lower latitudes and cooler temperatures in order to accommodate for the longer incubation time.

Squat lobster aggregation is theorized to be proportional to the amount of available organic particulate carbon reaching the seafloor. As such, many species of benthic squat lobsters aggregate into groups of very high population density around a number of different types of highly productive areas of the deep sea, like hydrothermal vents, cold seeps, sites of food falls like whale falls or wood falls, and shipwrecks. Squat lobsters seem to aggregate in these areas because they are associated with the fauna that thrives in them, like Bathymodiolus mussels and vestimentiferan tubeworms, but they are also attracted to the three dimensional structures found in them. Burrows, crevices, or debris from shipwrecks are suggested to serves as shelter against predators, as well as food accumulation sites. A variety of squat lobster called Emmunida picta were found to almost exclusively reside on some type of structure, mostly Lophelia pertusa. Squat lobster species found on seamounts typically have smaller bodies with shorter larval stages, as opposed to rise and ridge habitats. It has been suggested that this is due to the difference in substrates at these habitats.

Pleuroncodes planipes perform vertical migration into the water column from the benthos at different stages in development, an example of ontogenetic migration. Early larval stages are found mostly near the sea surface, but older larval and juvenile stages have a wide vertical distribution through the water column, and adults become almost purely benthic, with only a few vertical migrations in their remaining lifetime. In these migrations, they will form large swarms (up to 200 m vertically, and up to 10 km horizontally) in which they rely the selective tidal stream for feeding.

In a resting posture, squat lobsters rest their claws on the substrate in front of them. E. picta were observed most frequently in all conditions with their claws extended into the water column, perpendicular to the substrate. In the case of this study, the behavior was thought to be an avoidance response to the surveillance submersible, hence why this behavior was so often observed. In general, it is thought that this behavior may be a mechanism to increase the perceived size of the squat lobster as an aggressive or perhaps illusory display to ward off predators, as well as an active "fishing" strategy to catch prey. When aggressive displays do occur, as a result of competition for mates or food, the aggressive behavior is ignored 70% of the time, met with submission 20% of the time, and met with reciprocal aggression 10% of the time. These species of squat lobster also displayed very short interbrood intervals, or time between mating, generally not longer than a few days. As well as being used for human consumption, there is demand for squat lobster meat to be used as feed in fish farms and shrimp or prawn farms. This is in part because they contain astaxanthin, a pigment that helps to colour the meat of farmed salmon and trout. In Central America, the primary species of squat lobster targeted by fisheries is a species of Pleuroncodes. There is a great deal of confusion over both scientific names and common names, and the exact species is often unknown. In El Salvador, for instance, the commercial catch is generally referred to as "P. planipes", but is in fact P. monodon. Chirostyloidea contain the families Chirostylidae, Eumunididae, and Kiwaidae. Galatheoidea contain the families Galatheidae, Munididae, Munidopsidae, and Porcellanidae. The systematics of squat lobsters and the classification of deep sea squat lobsters is an area of active research due to the limited fossil record. Molecular and morphological data indicate that Galatheoidea is not a monophyletic group; Galatheidae, Porcellanidae, Kiwaidae, and Chirostylidae have independent origins. divided into over 900 recognized species; more than 120 undescribed species likely exist. It is likely that squat lobsters underwent deep sea colonization multiple times in evolutionary history. Squat lobsters underwent rapid diversification in the late Oligocene through the Miocene likely due to a variety of selection pressures, beginning in the Southwest Pacific. Fossil galatheoid squat lobsters have been found in strata dating back to the Middle Jurassic of Europe. No fossils are currently assigned to the Chirostyloidea. A split in the galatheid fauna exists between the Eastern Pacific, containing much less species richness, and the Western Pacific. The center of diversity for squat lobsters is the "coral triangle", or Indo Australian Archipelago, especially in the region of New Caledonia (with more than 300 species) and the region of Indonesia and the Philippines. High endemism is reported in this area and it is hypothesized this is due to many independent evolutions. This region results in high diversification due to global warming, tectonic activity, and oceanic currents. Modern regions of high speciation of squat lobsters includes seamounts near ocean trenches in the West Pacific, but squat lobsters are found in a range of habitats including continental shelfs, ridges, and abyssal seabeds. The hotspot distribution of squat lobsters in shallow waters seems to mirror the distribution of deep sea species.