Nymphon japonicum (English spelling) Nymphonjaponicum

...adults are generally free-living, but many species, such as the sandy sea spider Nymphonella tapetis , whose adults live on the sandy bottom of shallow waters and whose larvae live as parasites within the mantle cavities of clams, temporarily parasitize other animals. Shallow-water species are small, such as the zebra pygmy spider Lecythorhynchus hilgendorfi , which lives among seaweed roots and under stones near the shoreline and is about 5 mm in body length, and the long-toed pygmy spider Propallene longiceps , which is caught in plankton nets near eelgrass beds and is about 3 mm. However, some deep-sea species are large, such as the silkworm Nymphon japonicum , which lives at depths of 50 to 1000 m and has a body length of 1 to 1.5 cm and legs of 4 to 5 cm, and the red giant pygmy spider Colossendeis colossea (illustration), which was found at a depth of 4000 m and is known as the largest pygmy spider in the world (body length 9 cm, leg length 35 cm). About 500 species are known.

*Some of the terminology that mentions "Nymphon japonicum" is listed below.

Source | Heibonsha World Encyclopedia 2nd Edition | Information

…一般に成体は自由生活をするが，カイヤドリウミグモNymphonella tapetisのように成体は浅海の砂底にすみ，幼生がアサリの外套（がいとう）腔内で寄生生活をするなど，幼生が他の動物に一時的に寄生するものが多い。汀線（ていせん）付近の海藻の根の間や石の下にいるシマウミグモLecythorhynchus hilgendorfiは体長5mmくらい，アマモ場付近でプランクトン･ネットに入ってくるツメナガウミグモPropallene longicepsは約3mmなど浅海性の種は小型であるが，深さ50～1000mのイトユメムシNymphon japonicumは体長1～1.5cm，脚は4～5cmを有し，4000mの深さからもえられたベニオオウミグモColossendeis colossea（イラスト）は世界最大(体長9cm，脚の長さ35cmくらい)のウミグモとして知られるなど，深海性の種には大型となるものがある。500種ほどが知られている。…

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出典｜株式会社平凡社世界大百科事典 第２版について | 情報