Figure F5. A–D. Eurygonum nodosum (SEM images of resin casts of boreholes), a trace produced by the cyanobacterium Mastigocoleus testarum. The frequently bifurcated trace produces filamentous casts of variable diameter and develops characteristic lateral swellings, which harbor heterocysts (arrows), the nitrogen-fixing cells. B. Short lateral branch probably containing heterocysts (arrow). C, D. Variations in E. nodosum borings. E. nodosum is exclusively recorded in coral skeletons from Tahiti deglacial coral reefs.
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