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''Caprella mutica'', commonly known as the Japanese skeleton shrimp, is a species of skeleton shrimp. They are relatively large caprellids, reaching a maximum length of . They are sexually dimorphic, with the males usually being much larger than the females. They are characterized by their "hairy" first and second thoracic segments and the rows of spines on their bodies. Body color ranges from green to red to blue, depending on the environment. They are omnivorous highly adaptable opportunistic feeders. In turn, they provide a valuable food source for fish, crabs, and other larger predators. They are usually found in dense colonies attached to submerged man-made structures, floating seaweed, and other organisms. ''C. mutica'' are native to shallow protected bodies of water in the Sea of Japan. In as little as 40 years, they have become an invasive species in the North Atlantic, North Pacific, and along the coasts of New Zealand. They are believed to have been accidentally introduced to these areas through the global maritime traffic and aquaculture. Outside of their native range, ''C. mutica'' are often exclusively synanthropic, being found in large numbers in and around areas of human activity. Their ecological and economic impact as an invasive species is unknown, but they pose a serious threat to native populations of skeleton shrimp in the affected areas. ==Description== Like all caprellid amphipods, ''Caprella mutica'' are characterized by slender bodies and elongated appendages. Their skeletal appearance gives rise to the common names of "skeleton shrimp" or "ghost shrimp", and, coupled with their distinctive upright feeding posture, give them a striking resemblance to stick insects and "starved praying mantises". ''C. mutica'' vary in coloration from translucent pale green, brown, cream, orange, deep red, purple, and even turquoise, depending on the substrate they are found in. The brood pouches of the females are speckled with red spots.〔〔 A relatively large amphipod, ''C. mutica'' are sexually dimorphic with males considerably larger than females. Males average at a length of ,〔 though specimens have been recorded to reach in length.〔 Females, on the other hand, average at only long.〔〔(【引用サイトリンク】title=''Caprella mutica'' Schurin, 1935 – Japanese skeleton shrimp )〕 The body can be divided into three parts – the cephalon (head), the pereon (thorax), and the abdomen.〔 The pereon comprises most of the length of the body. It is divided into seven segments known as pereonites. The rounded and smooth cephalon is fused to the first pereonite; while the highly reduced and almost invisible abdomen is attached to the posterior of the seventh pereonite.〔〔 In males the first two pereonites are elongated, with the second pereonite being the longest of all the pereonites.〔 They are densely covered with long setae (bristles), giving them a hairy appearance.〔 The second pereonite also has two to three pairs of spines on the back, with an additional two pairs at the sides near the base of the limbs.〔 The remaining pereonites (third to seventh) lack the dense setae of the first two pereonites. The third pereonite has seven pairs of spines at the back while the fourth pereonite has eight pairs. Both have three to seven pairs of spines near the base of the gills. The fifth pereonite has five pairs of back spines and a pair of spines at the sides. The sixth and seventh pereonites each have two pairs of back spines, situated at their centers and near the posterior.〔 Females differ from males in having much shorter pereonites which lack the dense covering of setae. The cephalon and first pereonite also possess a single pair of spines each, though they can sometimes be absent.〔 Like other crustaceans, ''C. mutica'' possess two pairs of antennae, with the first (outer) pair more than half the total length of the body.〔 The segments of the peduncles (base) are three times as long as the flagellae ("whips" at the ends of the antennae). The flagellae have 22 segments each.〔 The second (inner) pair of antennae are less than half the length of the first. They possess two rows of long setae on the ventral surfaces of the segments of their peduncles.〔 Mandibles and maxillae are present at the anterior ventral surface of the cephalon. Maxillipeds, a modified pair of appendages, also serve as accessory mouthparts.〔〔 The appendages that arise from pereonites are known as pereopods. The first two pairs of pereopods are highly modified raptorial grasping appendages known as gnathopods. They somewhat resemble the arms of praying mantises. The segments of the gnathopods can be divided into two parts which fold into each other: the propodus (plural: propodi, "forelimb") and the tipmost segment known as the dactylus (plural: dactyli, "finger").〔 The first pair of gnathopods are considerably smaller than the second pair and arise close to the maxillipeds. The inside margins of the propodi possess two spines. Both the propodi and dactyli have serrated inner edges. The second pair of gnathopods are very large with two large spines on the middle and upper edges of the inside margin of the palm of the propodi.〔 The upper spine is known as the "poison spine" or "poison tooth" and may be of the same size or much larger than the lower spine (the "closing spine"). Despite the name, the poison spines are not known to be venomous, though they are perfectly capable of inflicting potentially lethal injuries on small organisms.〔 Their dactyli are powerful and curved into a scimitar-like shape.〔 The second pair of gnathopods are densely covered in hair-like setae while the first pair only has setae on the posterior margins.〔 The third and fourth pereopods are absent. In their place are two pairs of elongated oval gills arising from the third and fourth pereonites, respectively.〔 In mature females, two brood pouches also develop in the third and fourth pereonites. These are formed by oostegites – platelike expansions from the basal segments (coxae) of the appendages. The fifth to seventh pereopods function as clasping appendages. They all have propodi with two spines on their inside margins. The seventh pair of pereopods are the longest of the three pairs, followed by the sixth pereopod pair and the fifth pereopod pair.〔 ''C. mutica'' closely resemble ''Caprella acanthogaster'', also a native of East Asian waters. It may be difficult to distinguish the two species, particularly since ''Caprella mutica'' can exhibit considerable morphological variations among males. ''C. mutica'' can only be reliably differentiated by their setose first and second pereonites (smooth in ''C. acanthogaster''), as well as the elongated oval shape of their gills (linear in ''C. acanthogaster'').〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Caprella mutica」の詳細全文を読む スポンサード リンク
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