Fig. 1

Organization of the competent larvae of Phoronopsis harmeri. In all photographs, the apical side is to the top. a Whole larva viewed from the ventro-lateral side; SEM. b Photograph of a live larva viewed from the left. c Sagittal semithin section of whole larva; the ventral side is to the left. d Longitudinal semithin section of the preoral lobe of larva; the ventral side is to the left. e Longitudinal semithin section of the protonephridium, which bears upper and lower groups of terminal cells. Abbreviations: ao – apical organ; bc – blastocoel; bm – blood mass; bv – blood vessels; c – canal of protonephridium; c1 – protocoel; c2 – mesocoel; c3 – metacoel; d – diaphragm; dv – dorsal blood vessel; es – esophagus; lc2 – mesocoel lining; lg – lower group of terminal cells; m – mouth; mg – midgut; ms – metasomal sac; oms – opening of metasomal sac; pl – preoral lobe; sd – stomach diverticulum; st – stomach; t – tentacle; tt – telotroch; ug – upper group of terminal cells, vm – ventral mesentery