Figure 1.

The tropical didemnid ascidian L. patella in its natural habitat. (a) Inner coral reef crest at low tide on Heron Island, QLD, Australia. (b) Specimen of L. patella found nested within dead and living coral branches. (c) Deep-green specimen of L. patella, where the green coloration originates from its obligate symbiont Prochloron spp. that resides in the cloacal cavities of the ascidian. (d) Cross-section of L. patella. Note the thick reddish biofilm covering the underside of the tunic and the green Prochloron cells in the cloacal cavity of the ascidian. ‘Surface', ‘cloacal cavity' and ‘underside' denote the sites were samples were taken for subsequent analysis in this study.