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Title :海底洞窟に固有のSigillidae科貝形虫の起源と進化に関する研究
Title alternative :The study on the origin and evolution of sigillid ostracods characteristic of submarine caves
Authors :田吹, 亮一
Authors alternative :Tabuki, Ryoichi
Issue Date :May-2003
Abstract :平成12年度~平成14年度科学研究費補助金(基盤研究(C)(2))研究成果報告書
研究概要:Sigillidae科貝形虫(以、slgillids)は不等殻や多数の閉殻筋痕をする原始的なポドコピーダ目貝形虫だが、筆者は太平洋のサンゴ礁域において、公表済みのKasellaを含む洞窟固有のsigillidsの4新属を発見した。本研究では、sigillidsの全ての属の殻形質を属間で比較検討し、属間の類縁関係、洞窟性sigillidsの起源と進化について推定した。 sigillidsは殻表面の装飾の有無によりCardobairdia、Saipanetta、Genus Aのnon-ornate sigillidsとKasella、Genus B、Genus Cのornate sigillidsに二分しうる。non-ornate sigillidsの内、Cardobairdiaは右殻の蝶番が本来の蝶番要素からなり、ornate sigillidsに近い。Saipanetta、Genus Aは右殻の蝶番が二層構造を示す点で互いに近縁である。ornate sigillidsは殻外形、殻表面の模様、小筋痕の形態などから、Genus BがCardobairdiaに近く、Genus CはKasellaに近い一方でGenus Bと蝶番構造で一致する。Kasellaは多くの'advanced features'をもつ一方で、原始的な蝶番構造やこれまでCardobairdiaにだけみられた右殻後部の刺状突起を有するが、これは一種の'先祖返り'と考えられる。非洞窟性のCardobairdiaとSaipanettaのみ中生代以降の化石記録をもつが、この化石記録を重視する限り、洞窟に固有のsigillidsは非洞窟性のsigillids、又はそれに近縁な未知のsigillidsを祖先とするのが妥当である。Genus AはSaipanetta又はそれに近縁な貝形虫タクサ、Genus BはCardobairdia又はそれに近縁なタクサ、Genus CはGenus B又はそれに近縁なタクサ、KasellaについてはGenus C又はそれに近縁なタクサを祖先として進化した可能性が高い。本報告では殻形質をもとにした研究結果について述べたが、付属肢については研究を続行中で2年後を目処にその成果を公表する予定である。
要約(英文):Sigillids are primitive podocopid ostracods having unequal valves and many small adductor muscle scars. The author found four troglobitic sigillid genera, Kasella Tabuki and Hanai 1999 and three new genera of Genus A, B and C, from coral reefs in the Pacific. In this study, the author taxonomically examined the carapace features of all the sigillid genera in detail and tried to demonstrate the phylogenetic affinities among the genera and the origin and evolution of the troglobitic sigillids. Sigillids are classified into two taxonomical groups for the presence of ornamentation: the non-ornate sigillids composed of Cardobairdia, Saipanetta and Genus A, and the ornate sigillids of Kasella, Genus B and Genus C. Cardobairdia is close to the ornate sigillids in having the 'original hingement' in the right valve. Saipanetta and Genus A differ from the other genera in having the 'two-layered hingement'. The ornate Genus B is closer to Cardobairdia in lateral outline and shape of adductor scar. Genus C shares many key carapace features not only with Kasella, but also with Genus B. While Kasella has many 'advanced carapace features', it shows the features possibly resulted from so-called reversion such as a posteroventral spine on the right valve appeared also in Cardobairdia and a primitive hingement structure similar to that of healdioideans. Only the non-troglobitic sigillids, Cardobairdia and Saipanetta, have the fossil records since the Jurassic. This fact suggests that the troglobitic sigillids derived from the non-troglobitic sigillids. The Genus A possibly derived from Saipanetta or its relatives. Genus B is thought to have originated from Cardobairdia or its relatives, Genus C from Genus B or its relatives and Kasella from Genus C or its relatives.
Type Local :研究報告書
Publisher :田吹亮一
URI :http://hdl.handle.net/20.500.12000/13592
Appears in Collections:Research Report (Faculty of Education)

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