Fig. 1
Electron microscopy (EM) micrograph of adult sponge brooding larvae of Thoosa mismalolli. (A) Scanning electron microscopy (SEM) of a brood chamber (bch) with an immature larva (il) reveals the presence of a single layer of imbricate monoaxonic flat disc spicules (s) and protruding extensions (pe) in development. (B) Transmission EM section of mesohyl (ml) of parental sponge tissue and brooded larva (bl). Note the follicular epithelium (fe) and nurse cells (nc) surround the brooded larva and the regional differentiation of the larval body (white arrows; OZ: outer zone, MZ: middle zone, IZ: inner zone). (C) Microsclerocyte (scl) with long cytoplasmic processes (like pseudopodia; ps) around a cross-sectioned, highly fractured monoaxonic flat discs (spicule; s). Note the accumulation of collagen fibrils (cf) around the spicule (s) and the extracellular bacteria (eb). (D) Detail of gray cell (gc) of the peripherical layer in the MZ. Note the prominent anucleolate nucleus (n) and numerous yolk granules (y), lipid droplets (l), and dispersed granules of glycogen (gly). (E) Detail of MZ contains spherulous cell (spc), bacteriocytes (bac) and archeocytes (arc). Note abundant glycogen (gly) aggregation. (F) Detail of archeocyte showing the multiple (6) Golgi complexes (g) adjacent to the membrane of the nucleus (n). (G) Cytoplasmic contents of bacteriocyte. Note the numerous phagosomes (pg) with 1–3 bacteria (b) and the abundant glycogen (gly) aggregation in granular electrodense inclusions around the phagosomes. (H) Choanocyte chamber (chc) lined by flattened pinacocytes (pl). Note that the zone directly surrounding the pinacocyte layer (pl) becomes densely populated with extracellular bacteria (eb), some of which are undergoing binary fission (white arrows).
