Fig. 2

Ontogeny of the scaphopod Antalis entalis. All lateral views and dorsal (d)–ventral (v), anterior (a)–posterior (p) axes indicate the orientation. Note the prototroch (dark gray), the statocysts (black dashed encircled), the apical organ (red dashed circle) with serotonin-like immunoreactive cells (red) and apical tuft (at), the cerebral ganglia (blue) and the pedal ganglia with connectives (green). The mouth (mo) is located ventrally to the foot (f), while the anus (an) is located ventrally to the pavilion (pv; dorsal mantle opening). The light blue line outlines the shell. a Gastrula with blastopore (bp) (12 hpf). b The early-stage trochophore (14 hpf) exhibits an episphere (ep) with an apical organ with two serotonin-like immunoreactive cells. The prototroch (pt) divides the episphere from the hyposphere (hp). In the anterior hyposphere, the shell field (shf) develops. c Mid-stage trochophore (21 hpf) possesses four serotonin-like immunoreactive cells in addition to two lateral cells (not shown) that do not belong to the apical organ. d Late-stage trochophore (63 hpf). e Metamorphic competent trochophore (70 hpf). f Postmetamorphic and settled specimen (114 hpf). Data on serotonin-like immunoreactive cells and on the location of the CNS derive from [36–38, 40]. cp captacula, mg midgut gland. Scale bars 50 µm