Kikuitaboya - Kikuitaboya

A colonial ascidian belonging to the order Wallea of ​​the class Urichordata of the phylum Protochordata and the family Botryllidae. It generally forms sheet-like colonies about 2 mm thick. Numerous zooids are embedded almost vertically in a colorless, transparent common integument. Five to seven zooids gather in a star shape around a common excretion hole, but in some colonies, zooids with an excretion hole directly on the surface of the common integument can be seen. When alive, zooids are often colorfully colored with a reddish-brown base. Each zooid is connected by a dense mesh of encysting blood vessels that run through the common integument. The gill pouch has three longitudinal blood vessels on each side and four gill slit rows. The ovary is located ventrally and contains one large egg, and the testes are located posterior to it. It is widely distributed from the intertidal zone to shallow waters off the coast of Japan, and also appears on the coast of California and the coast of the western Pacific Ocean.

[Teruaki Nishikawa]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

原索動物門尾索綱壁性目ボトリルス科に属する群体ボヤ。一般に厚さ2ミリメートル程度のシート状の群体をつくる。無色透明の共同外皮の中に多数の個虫がほぼ垂直に埋まる。5～7個虫が一つの共同排出孔を囲んで星形に集合するが、出水孔が直接共同外皮表面に開口する個虫が群体の一部にみられることがある。個虫は生時赤褐色を基調に多彩に彩られることが多い。各個虫は共同外皮中を網目状に密に走る被嚢(ひのう)血管で結ばれる。鰓嚢(さいのう)内の縦走血管は各側に3本、鰓孔列は4個。卵巣は腹方にあって大きな1卵を含み、精巣はその後方に位置する。日本沿岸の潮間帯から浅海に広く分布するほか、カリフォルニア沿岸や西太平洋の沿岸にも出現する。

［西川輝昭］

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