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Acrosphaera australis Lazarus, 1990

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Smooth, hyaline sphere with large, irregularly spaced and shaped pores extended outwards radially into tubes; tube tips flared and in many of the pores joined to adjacent tube tips to form outer layer of hyaline bands or bridges between tube tips.

Distinguished from other collosphaerids by the presence of an outer layer of elevated bands joining tube tips. Evolves from Acrosphaera murrayana (Haeckel) Strelkov and Reshetnyak, 1971 by the joining together of the flared tips of the tubes. This evolutionary transition is clearly seen in Leg 113 material, with transitional specimens being quite common in populations at the base of A. australis' range. The first appearance is defined by the first occurrence of specimens with more than one pair of pores joined by well developed bands. Specimens of A. murrayana still occur in these early, transitional populations. The generic assignment follows the revisions of Strelkov and Reshetnyak (1971) and Bjørklund and Goll (1979), which divide the collosphaerids into genera based on the presence or absence of tubes or spines. As noted by Bjørklund and Goll, even the current generic divisions in the collosphaerids are artificial, as evolutionary transitions between spinose, tubular, and unornamented forms are seen in fossil lineages. This is true in particular of the Acrosphaera murrayana - A. australis lineage, since A. murrayana is a spinose form, while A. australis is a tubular one. Acrosphaera is retained however until a better generic taxonomy for the collosphaerids becomes available.
Lazarus 1990











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