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Squat lobster
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Squat lobster
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. If one considers the members of the family Aeglidae as squat lobsters, then those numbers rise to more than 1000 species in 61 genera, and they occur at an altitude up to 3600 meters above the sea level. 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 18 to 89 millimetres (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 90 millimetres (3.5 in) in the case of Munidopsis aries, down to only a few millimetres in the case of Galathea intermedia and some species of Uroptychus. As in other decapod crustaceans, the bilaterally symmetrical body of a squat lobster may be divided into two main regions: the cephalothorax (itself made up of the cephalon, or head, and the thorax), and the pleon or abdomen. The pleon only being partly flexed under the cephalothorax and the cephalothorax being more long than it is broad makes the squat lobster a morphological intermediate between a lobster and crab.
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. The cephalothorax is covered with a thick carapace, which may extend forwards in front of the eyes to form a rostrum; this is highly variable among squat lobsters, being vestigial in Chirostylus, wide and often serrated in some genera, and long, narrow, and flanked with "supraorbital spines" in others. The degree of ornamentation on the surface of the carapace also varies widely, and there are almost always at least a few setae (bristles), which can be iridescent in some members of the Galatheidae and Munididae. A pair of compound eyes also project on stalks from the front of the carapace; these are made up of ommatidia with square facets, which is typical of the "reflecting superposition" form of eye. Many deep-sea species have reduced eyes, and reduced movement of the eyestalks. In the families Munididae and Galatheidae, there is often a row of setae close to the eyes, forming "eyelashes".
The mouthparts consist of six pairs of appendages— three posterior cephalic appendages and the first three pairs of thoracic appendages. While their function was traditionally believed to be limited to food handling, the mouthparts have a more complex movement pattern that allows them to perform a variety of functions such as prey- and sediment-gathering, sediment transfer, and sediment sorting/particle rejection. In Munida sarsi, the farther the mouthparts are located from the mouth, the more complex in movement and functional scheme they are.
The most conspicuous appendages are the pereiopods, and the largest of these is the first pair. These each end in a chela (claw), and are therefore known as the "chelipeds"; they can be more than six times the body length, although some groups show sexual dimorphism, with females having proportionally shorter chelipeds. The following three pairs of pereiopods are somewhat smaller than the chelipeds and are without claws, but are otherwise similar; they are used for walking. The fifth pair of pereiopods are much smaller than the preceding pairs, and are held inconspicuously under the carapace. They each end in a tiny chela, and are generally believed to be used for cleaning the body, especially the gills, which are in a cavity protected by the carapace.
The pleon is made up of six somites, each bearing a pair of pleopods, and terminating in a telson. The first somite is narrower than the succeeding somites, and the last pair of pleopods are modified into uropods, which flank the telson. The pleon is usually curled under the thorax, such that only the first three somites are visible from above. The form of the pleopods varies between the sexes. In females, the first one or two pairs are missing, while the remaining pairs are uniramous, and have long setae, to which the eggs can be attached. In males, the first two pairs are formed into gonopods, and are used to transfer the spermatophore to the female during mating; the first pair is often missing. The remaining pleopods can be similar to those of the females, or reduced in size, or entirely absent. In both sexes, the uropods are biramous.
Carcinisation has previously been explored in regards to outer morphology; however, the external change in body shaped has influence on the internal anatomical features as well. The use of micro-computer tomography and 3D reconstruction have brought to light anatomical disparity within Galatheoidea. Differences have been found in the ventral vessel system between porcelain crabs and squat lobsters. Carcinisation is also responsible for the loss of the caridoid escape reaction which caused a shift in gonads and the pleonal neuromeres for squat lobsters.
Fecundity, or number of eggs, increases with smaller sized eggs and increasing body size of the parent. This results in increasing incubation time and consequently, increased egg volume. 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.
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Squat lobster
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. If one considers the members of the family Aeglidae as squat lobsters, then those numbers rise to more than 1000 species in 61 genera, and they occur at an altitude up to 3600 meters above the sea level. 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 18 to 89 millimetres (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 90 millimetres (3.5 in) in the case of Munidopsis aries, down to only a few millimetres in the case of Galathea intermedia and some species of Uroptychus. As in other decapod crustaceans, the bilaterally symmetrical body of a squat lobster may be divided into two main regions: the cephalothorax (itself made up of the cephalon, or head, and the thorax), and the pleon or abdomen. The pleon only being partly flexed under the cephalothorax and the cephalothorax being more long than it is broad makes the squat lobster a morphological intermediate between a lobster and crab.
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. The cephalothorax is covered with a thick carapace, which may extend forwards in front of the eyes to form a rostrum; this is highly variable among squat lobsters, being vestigial in Chirostylus, wide and often serrated in some genera, and long, narrow, and flanked with "supraorbital spines" in others. The degree of ornamentation on the surface of the carapace also varies widely, and there are almost always at least a few setae (bristles), which can be iridescent in some members of the Galatheidae and Munididae. A pair of compound eyes also project on stalks from the front of the carapace; these are made up of ommatidia with square facets, which is typical of the "reflecting superposition" form of eye. Many deep-sea species have reduced eyes, and reduced movement of the eyestalks. In the families Munididae and Galatheidae, there is often a row of setae close to the eyes, forming "eyelashes".
The mouthparts consist of six pairs of appendages— three posterior cephalic appendages and the first three pairs of thoracic appendages. While their function was traditionally believed to be limited to food handling, the mouthparts have a more complex movement pattern that allows them to perform a variety of functions such as prey- and sediment-gathering, sediment transfer, and sediment sorting/particle rejection. In Munida sarsi, the farther the mouthparts are located from the mouth, the more complex in movement and functional scheme they are.
The most conspicuous appendages are the pereiopods, and the largest of these is the first pair. These each end in a chela (claw), and are therefore known as the "chelipeds"; they can be more than six times the body length, although some groups show sexual dimorphism, with females having proportionally shorter chelipeds. The following three pairs of pereiopods are somewhat smaller than the chelipeds and are without claws, but are otherwise similar; they are used for walking. The fifth pair of pereiopods are much smaller than the preceding pairs, and are held inconspicuously under the carapace. They each end in a tiny chela, and are generally believed to be used for cleaning the body, especially the gills, which are in a cavity protected by the carapace.
The pleon is made up of six somites, each bearing a pair of pleopods, and terminating in a telson. The first somite is narrower than the succeeding somites, and the last pair of pleopods are modified into uropods, which flank the telson. The pleon is usually curled under the thorax, such that only the first three somites are visible from above. The form of the pleopods varies between the sexes. In females, the first one or two pairs are missing, while the remaining pairs are uniramous, and have long setae, to which the eggs can be attached. In males, the first two pairs are formed into gonopods, and are used to transfer the spermatophore to the female during mating; the first pair is often missing. The remaining pleopods can be similar to those of the females, or reduced in size, or entirely absent. In both sexes, the uropods are biramous.
Carcinisation has previously been explored in regards to outer morphology; however, the external change in body shaped has influence on the internal anatomical features as well. The use of micro-computer tomography and 3D reconstruction have brought to light anatomical disparity within Galatheoidea. Differences have been found in the ventral vessel system between porcelain crabs and squat lobsters. Carcinisation is also responsible for the loss of the caridoid escape reaction which caused a shift in gonads and the pleonal neuromeres for squat lobsters.
Fecundity, or number of eggs, increases with smaller sized eggs and increasing body size of the parent. This results in increasing incubation time and consequently, increased egg volume. 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.
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