Fig. 1. (A) Sagittal section showing the body parts of the whole vestimentiferan tubeworm Riftia pachyptila and the labeling of total RNA by Gallocyanin. The four main body compartments of the worm are indicated, with their respective RNA synthesis activity. (B) Corresponding densitometry analysis of the section processed with NIH Image, with a binary transform at 50% threshold. Maximal transcription activity was detected in the trophosome lobules, at the basis of the joined branchial lamellae and in the epithelium of the wings. The obturaculum, vestimentum and body wall showed basal expression levels. Scale bar, 2 mm.