Studies on Japanese Xenoturbella for the understanding of early evolution of Bilateria

2023 Fiscal Year Final Research Report

• Project/Area Number: 19H03279
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 45030:Biodiversity and systematics-related
• Research Institution: University of Tsukuba
• Principal Investigator: Nakano Hiroaki 筑波大学, 生命環境系, 准教授 (70586403)
• Project Period (FY): 2019-04-01 – 2024-03-31
• Keywords: 珍渦虫 / 無腸動物 / 珍無腸動物 / 新口動物 / 左右相称動物 / 後生動物 / 進化 / 自然史

Outline of Final Research Achievements

Xenoturbella is a benthic marine animal lacking anus, centralized nervous system, and coeloms. It has been suggested that this simple body plan of the animal may have been retained from the last common ancestor of bilaterians. Therefore, Xenoturbella is important for evolutionary studies on Metazoa. However, its development and reproduction has not been fully elucidated. In this study, we report the spawning of the animal, using a newly established artificial spawning induction method. Xenoturbellids were revealed to be gonochoric with external fertilization. We also performed phylogenomic analyses on the animal, with the results suggesting that it is a member of the deuterostomes. A microCT method was established for xenoturbellids, enabling observations on internal structures non-destructively. Placozoans, acoelomorphs, and nudibranchs were studied for comparisons with xenoturbellids, and major findings were gained for each animal respectively.

Free Research Field

進化動物学

Academic Significance and Societal Importance of the Research Achievements

珍渦虫の研究から左右相称動物の起源に関する新知見が得られることが期待される。本研究で放卵放精誘起法を確立したことから、珍渦虫の発生に関する研究が大きく進展すると考えられる。確立したmicroCTによる非破壊的観察法は、珍渦虫の形態学的研究に大きく貢献する。本手法は他の海産無脊椎動物にも応用可能であり、海洋生物学に大いに役立つ。本研究で新種記載した無腸動物には他の無腸動物にはない背面突起を有し、本種は初期の左右相称動物における新奇形質獲得研究のモデルケースとなりうる。また、本研究で開発したイロウミウシ科の発生系は、今後の研究の基盤となるだけではなく、水族館等での展示にも応用可能であると考える。