Figure 3

Early developmental stages of Buddenbrockia. (A) Light microscopy micrograph showing spherical as well as small, wormlike stages (arrowheads) attached to a gut dissected from Fredericella sultana. (B) Detail of (A) as indicated by rectangle. Confocal section merged with transmitted light microscopy micrograph showing details of tissue organisation. (C) Three-dimensional volume rendering of confocal image stack showing attachment to host tissue and host tissue reaction (double arrowheads). The tip of the worm is surrounded by slightly enlarged peritoneal cells that form cytoplasmic extensions with a higher actin content. (D) through (I) Early wormlike stages free-floating in body cavity of Plumatella sp. (D) Light micrograph. (E) through (I) Maximum-intensity projections of confocal microscopy image stacks showing tissue differentiation at the distal tip. (F) and (G) Confocal microscopy optical cross-sections through worm similar to the one shown in (E). (F) Proximal end with compact mass of inner cells. (G) and (H) In the middle region and distal region, the inner cells have formed an epithelial layer encompassing a central lumen. Few cells (arrowheads), representing the muscle precursors, become situated in an intercalary position between the two epithelial layers. F-actin (green); nuclei (red); cl, central lumen; dt, distal tip; ep, epidermis; gu, bryozoan gut; ic inner cells; ie, inner epithelium; mc, myocyte; pt, proximal tip.