Fig. 11

Development of ciliary bands and juvenile in pilidium nielseni. a. “Pileus” stage of pilidium nielseni with four separate segments of ciliary bands, corresponding to the anterior lobe (al), posterior lobe (pl), and the two lateral lappets (lp). Larval ciliary cirrus (lc) is underneath the posterior lobe. Dash line outlines apical organ (ap) and gut (gt). All eight juvenile rudiments (solid thin outlines) are already present. b. Comparable developmental stage of a typical planktotrophic pilidium. Continuous primary larval ciliary band spans the larval lobes and lappets, eight juvenile rudiments are present. Other ciliary bands of the typical planktotrophic pilidium (inner ciliary bands on lappets, esophageal ciliary ridges) are omitted for clarity. c. Advanced developmental stage of pilidium nielseni with a complete juvenile and two transverse circumferential ciliary bands. Juvenile head (jh) is at upper left. d. Comparable developmental stage of a typical planktotrophic pilidium. Juvenile head to the left. In both types of larvae juvenile posterior ends up near the larval ciliary cirrus