Fig. 2

Morphology of a freshly hatched W. argentea larva. Dorsal (d)–ventral (v), left (l)–right (r), and anterior (a)–posterior (p) axes indicate the orientation. a Optical section of an autofluorescence scan of a freshly hatched test cell larva with anterior facing up. Dashed line indicates the prototroch, which separates the episphere (ep) from the hyposphere (hy). b 3D volume rendering based on an autofluorescence scan. Posterior view on the larval hyposphere and the invagination of the pseudo-blastopore of the same specimen as in (a). Abbreviations: cells of the apical organ (ao); episphere (ep); hyposphere (hy); lateral depression (ld); nucleus (n); pseudo-blastopore (pb); trochoblast (tb); test cell (tc); the two most posteriorly and laterally positioned test cells (arrowhead). Scale bars: 50 μm