The fine structures of some living Spyrida (Nassellaria, Radiolaria) and their implications for nassellarian classification

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概要

• 論文の詳細を見る

• Cytological structures of the two spyrids Acanthodesmia vinculata (Muller) and Lithocircus reticulatus (Ehrenberg) were examined. The cytological features of the two species are obviously different. A. vinculata has a pear-shaped central capsule containing an eccentrically situated nucleus and juxtanuclear axoplast. The fusules are concentrated around the base of the central capsule in a pore field (porocora), which is the most diagnostic feature of nassellarian cytology. In contrast, L. reticulatus possesses a globular central capsule containing a large centrally located nucleus. Of particular interest, fusules of L. reticulatus are distributed radially, all around the central capsule, which previously has been described as a typical feature of spumellarians, not nassellarians. In addition, there are some minor differences in ultrastructure of the capsular wall and fusules between the two spyrids. This evidence indicates that these two species should be separated above the generic level. Beyond these fine structural differences, the two spyrids have some common features of the capsular wall and fusule structure. Their capsular wall is considerably thicker (0.3-0.5μm thick) and multilayered compared to that of the cyrtid capsular wall that is composed of a single osmiophilic layer (0.03-0.05μm thick). Moreover, the spyrid fusules lack an inner osmiophilic zone that is characteristic of the cyrtid fusules. The general shape of the fusules is also different between the spyrids and cyrtids. These features are sufficiently different to validate the suborders Spyrida and Cyrtida as the highest hierarchical division among the nassellarians, and do not support assigning spyrids to a family taxon such as Acanthodesmidae or Trissocyclidae as previously suggested by some workers. The Spyrida and Cyrtida include respectively two and four types of nucleus-axoplast relationships, which appear to be useful for considering family classification. Among them, one relationship named Acanthodesmia-type is recognized both in the Spyrida and Cyrtida. This clearly suggests that convergence occurs frequently in radiolarian evolution. Hence, it is necessary to synthesize cytological, morphological and stratigraphic information to construct a consistent classification scheme of nassellarians.

• 日本古生物学会の論文
• 1998-06-30

著者

• SUGIYAMA KAZUHIRO

  Marine Geology Department, Geological Survey of Japan

• Anderson Roger

  Lamont-doherty Earth Observatory Of Columbia University

• Sugiyama Kazuhiro

  Marine Geology Department Geological Survey Of Japan

• Anderson O.Roger

  Lamont-Doherty Earth Observatory of Columbia University

関連論文

• Regular axopodial activity of Diplosphaera hexagonalis Haeckel (spheroidal spumellarian, Radiolaria)
• The fine structures of some living Spyrida (Nassellaria, Radiolaria) and their implications for nassellarian classification
• Pseudopodial features and feeding behavior of living nassellarians Eucyrtidium hexagonatum Haeckel, Pterocorys zancleus (Muller) and Dictyocodon prometheus Haeckel
• Replacement names for Permian stauraxon radiolarians

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