Expulsion of symbiotic algae by apocrine secretion and exocytosis during feeding by <i>Chlorohydra</i>.

<p>en = endoderm, gvc = gastrovascular cavity. A) A general view of the apical part of <i>Chlorohydra</i> endoderm, 15 minutes after feeding. A large membrane-bound “aposome” is seen within the GVC, adjacent to the apical membrane of an endodermal digestive cell. (black arrowhead). A symbiotic alga is in the process of exocytosis from the aposome (enlarged in the inset), and several others are seen in the apical part of the endoderm (white arrowheads). Bar = 10 µm (1 µm in the inset). B) Expulsion of alga during apocrine secretion, 15 minutes after feeding. Note heterogenous aposomes within the GVC (black arrowheads), one of which contains an alga (algae are marked by white arrowheads). Bar = 10 µm. C) Enlargement of the aposome marked by an square in B. The aposome contains one intact alga (in the process of exocytosis, white arrowhead), as well as possibly another being digested (grey arrowhead). * = mitochondria. Bar = 5 µm. D) An aposome containing four symbiotic algae within the GVC (white arrowheads). Note the microvilli seen on the apical membrane of an endodermal cell (black arrowhead). Bar = 10 µm.