Regularity in budding mode and resultant growth morphology of the azooxanthellate colonial scleractinian Tubastraea coccinea |
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Authors: | A Sentoku Y Ezaki |
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Institution: | (1) Department of Geosciences, Graduate School of Science, Osaka City University, 3-3-138 Sugimoto-cho, Sumiyoshi-ku, Osaka 558-8585, Japan |
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Abstract: | Scleractinia exhibit a variety of growth forms, whether zooxanthellate or azooxanthellate, according to factors that control
asexual reproduction and ensuing coral growth. The azooxanthellate branching scleractinian Dendrophyllia
arbuscula shows regular modes of budding in terms of the locations of budding sites, the orientations of directive septa, and the inclination
angle of budding throughout colonial growth. This study reports that such regularities are also found in the apparently different
growth form of the massive dendrophylliid Tubastraea
coccinea, which shows the following growth features: (1) the offsets (lateral corallites) always occur near four primary septa, except
the two directive primary septa, meaning that the lateral corallites do not appear in the sectors of the two directive septa;
(2) the two directive septa in lateral corallites tend to be oriented subperpendicular to the growth direction of the parental
corallites; (3) the lateral corallites grow approximately diagonally upwards; and (4) these regularities are seen in the axial
and derived lateral corallites among all generations during colony growth. Large differences in growth form are found between
the branching D.
arbuscula and massive T.
coccinea, irrespective of the presence of specific regularities. It is likely that subtle modifications of certain parameters (e.g.,
budding interval, branch length, corallite size, and inclination angle of lateral corallites) have a strong effect on the
overall growth morphology. A precise understanding of such regularities, which occur regardless of generation or taxonomic
position, would contribute to understanding the “shape-controlling mechanism” of corals, which are an archetypal modular organism. |
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