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Observation of radiolarians and their symbionts : On discoidal Spumellarida

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  • 放散虫と共生生物の観察 : 平板状の Spumellarida 目について
  • ホウサンチュウ ト キョウセイ セイブツ ノ カンサツ ヘイバンジョウ ノ S

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Light microscopic observation of discoidal Spumellarida and their symbionts reveals that species belonging to the Family Spongodiscidae, Dictyocoryne truncatum, Dictyocoryne profunda, Hymeniastrum euclidis, Spongaster tetras, and Spongodiscus sp., commonly possess reddish-brown symbiotic bacteria (<1.5μm in diameter). Euchitonia elegans of the Family Porodiscidae has both yellow symbiotic algae (5-8μm in diameter) and symbiotic bacteria. The number of symbionts and their distribution pattern in the host differ among species, suggesting that the observation of symbionts is useful in distinguishing species which have a morphologically similar shell. Laboratory-cultured radiolarian specimens move their symbiotic bacteria to the axopodia which are located near the light source, strongly suggesting that the symbiotic bacteria are photosynthetic organisms and that the host radiolarians transport them towards the light source to enhance their photosynthesis activity. Symbiotic algae and bacteria of E. elegans differ in their relationship with the host ; the former disappears while the latter remains within the host when the host becomes weakened or dies. This indicates that the symbiotic algae are ectosymbionts and that the symbiotic bacteria are endosymbionts.


  • Fossils

    Fossils 53 (0), 20-28, 1992

    Palaeontological Society of Japan

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