Karappa (box crab)

A general term for crabs of the genus Calappa , family Calappa, order Decapoda, class Crustacea, phylum Arthropoda. Formerly known as Manjugani, this crab is classified as Atergatis in the family Xanthopodidae, so to avoid confusion, the genus Calappa was adopted as the Japanese name. It is widely distributed in temperate and tropical seas around the world, and generally lives on the sandy and muddy bottoms of shallow seas. Its carapace is 5-15 cm wide and its back is dome-shaped, with a smooth and shiny surface or one that is covered with cone-shaped or slightly scaly protrusions. The front edge of the carapace is simply curved, but the rear edge juts out like a roof, allowing the walking legs to be folded underneath. Its claws are wide and completely cover the front of the carapace and the mouth. The claws on both sides are roughly the same size, but are different in shape, with a large protrusion at the base of the right immobile finger. The crab hooks this protrusion onto the opening of the snail, and, like a can opener, cuts and breaks the snail's coils, eating the hermit crab inside. It is said that the large claws help purify breathing water, and that the crab can store breathing water in a depression on the underside of the eaves-like protrusion of the shell.

There are 11 species of carappa found in Japan, but there are many individuals of the tiger-striped trout carappa C. lophos , which has a deep purple tiger stripe pattern, and the spectacled carappa C. philargius , which has a black-rimmed eye socket, and these are often caught in nets. There are also many species of the Japanese carappa C. japonica , which has reddish purple wart-like protrusions all over its surface, and the round-striped carappa C. calappa , which has a smooth shell with rounded projections, found in shallow waters. There are many species of the long-striped carappa C. hepatica , whose colors blend in with the sandy areas of coral reefs. They are sometimes dried and used as ornaments, but are not edible.

[Masamichi Takeda]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

節足動物門甲殻綱十脚(じっきゃく)目カラッパ科カラッパ属Calappaのカニ類の総称。古くはマンジュウガニとよばれていたが、オウギガニ科にマンジュウガニ属Atergatisとしてまとめられるカニ類があり、混乱を避けるために属名をそのまま和名とするようになった。世界の温帯、熱帯海域に広く分布し、一般に浅海の砂泥底にすんでいる。甲幅は5～15センチメートルで、背面がドーム形に膨れ、表面が滑らかで光沢がある場合と、円錐(えんすい)形またはやや鱗(うろこ)状の突起で覆われている場合がある。甲の前側縁は単に湾曲しているだけであるが、後側縁は屋根のひさし状に張り出し、その下に歩脚を折り畳むことができる。はさみ脚(あし)は幅広く、甲の前面や口の部分をすっぽり覆ってしまう。はさみ脚は左右ほぼ同大であるが、形は異なり、右側の不動指の付け根に大きな突起がある。この突起を巻き貝の入口にひっかけ、缶切りの要領で、巻いているのにあわせて切り壊してしまい、内部のヤドカリを食べる。大きなはさみ脚が呼吸水の浄化に役だつといわれ、また、甲のひさし状に張り出した下側のくぼみに呼吸水を蓄えておくことができるという。

　日本産のカラッパ類は11種であるが、濃紫色の虎斑(とらふ)模様をもつトラフカラッパC. lophosや、眼窩(がんか)が黒く縁どられているメガネカラッパC. philargiusは個体数が多く、網によくかかる。また、一面に赤紫色のいぼ状突起があるヤマトカラッパC. japonicaや、甲面が滑らかで張り出しが丸いマルソデカラッパC. calappaが浅海に少なくない。サンゴ礁の砂地にはじみな色彩のソデカラッパC. hepaticaが多い。乾燥させて置物などにされることはあるが、食用にはならない。

［武田正倫］

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