Fig. 1

The encrusting tropical sponges Plakortis angulospiculatus (HMA, a–c) and Halisarca caerulea (LMA, d–f). Electron micrographs illustrating differences in the size and abundance of sponge-associated microbes (TEM, b and e), and density of choanocytes in choanocyte chambers (SEM, c and f), between the HMA and LMA species. c, choanocyte; gr, electron dense granule; m, mesohyl cell; me, mesohyl; n, nucleus; sc, spherulous cell. Dashed lines delineate choanocyte chambers and black arrows indicate sponge-associated microbes. P. angulospiculatus photograph kindly provided by Sara Campana