Spirula - Spirula (English spelling)

A squid of the family Toglocoika in the class Cephalopoda of the phylum Mollusca. Its Japanese name is Toglocoika, and this species alone constitutes a single family. The English name for the shell alone is Ram's Horn Shell. It is found in the mid-depths of the Pacific, Indian and Atlantic Oceans, where the water temperature is below 10°C, and is collected from depths of 100 to 400 meters. When it dies, its shell floats to the surface and washes up on the shore, so it has been known since ancient times, but in 1910, the first living individual was discovered near the Canary Islands in the Atlantic. Its shell is 30 mm in long diameter and 7 mm in diameter at the opening, and unlike the carapaces (shells) of other squids, it is tubular and coiled. The tube gradually thickens and has many small chambers connected together, with an adult shell having about 25 chambers. The shell is also coiled ventrally, not dorsally like the nautilus. The soft body reaches a length of 70 mm, and has small fins on both sides of the rear end of the cylindrical mantle, with a light-emitting organ in the depression between them. The rolled shell is inside the mantle, located dorsoventrally at the rear end. It has eight short legs and a pair of long, slender tentacles. It lives for about a year, and has a long breeding period.

[Takashi Okutani]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

軟体動物門頭足綱トグロコウイカ科のイカ。和名をトグロコウイカといい、本種だけで1科をなす。殻のみに対してはram's horn shellの英名がある。太平洋、インド洋、大西洋の水温10℃以下の深海中層に分布し、水深100～400メートルの範囲から採集される。死ぬと殻は浮上して海岸に打ち上げられるので、古くから殻は知られていたが、1910年に大西洋のカナリア諸島近海で初めて生きた個体が発見された。殻は長径30ミリメートル、殻口径7ミリメートルに達し、ほかのイカ類の甲（貝殻）と異なり、管状で巻く。管は緩やかに太くなり、多くの小室が連なって、成貝では約25室ある。また殻は、オウムガイ類のように背方でなく、腹方へ巻く。軟体は体長70ミリメートルに達し、円筒状の外套(がいとう)の後端に、左右に小さいひれがあり、その間のくぼみに発光器がある。巻いた殻は外套内にあり、後端の背腹に位置する。足は短いのが8本あるほか、細長い触腕が1対ある。生存期間は1年ぐらいで、繁殖期間は長い。

［奥谷喬司］

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