Ultrastructure of the internal bud inside the attached Prometheus larva of <i>Symbion pandora</i>.

<p>SEM-SBF micrographs, longitudinal section. (<b>A</b>) The internal bud is located anteriorly in the attached Prometheus larva, ventrally to the young male (ym). In this cluster, all cells look similar to each other except for two cells (marked with an asterisk) that appear to interact by means of pseudopodia (arrow). <b>(B)</b> Detail of the two cells interacting by pseudopodia. Note that the nuclear membrane of these cells is more irregular as compared to the other cells. <b>(C)</b> Detail of a cell (marked with two asterisks) characterized by a disrupted nuclear membrane (arrowhead). <b>(D)</b> The internal bud is outlined only by a basal lamina (double arrowheads). Note also the presence of a cell (marked with two asterisks) with a disrupted nuclear membrane. Abbreviations: cu_P cuticle of the attached Prometheus larva, nu nucleus.