Fig. 6.

Contrasting mechanisms of isotopically labelled DOM (a–c) and POM (d–f) incorporation by choanocytes of the LMA species H. caerulea. Correlated NanoSIMS (a, d) and SEM images (b, e) with partial ¹⁵N-signal overlay (c, f) show the rapid internalisation of ¹⁵N labelled DOM and POM after 0.5 h and 0.25 h, respectively. DOM is incorporated into the apical tip of choanocytes (arrows), while food bacteria are phagocytosed by these filtering cells. The colour scale in a and d represents enrichment relative to natural abundance ratios (in blue, 0.0037). f, food bacteria; v, intracellular vesicle. Scale bars are 1 μm