Figure 2.

Early swimming larva (Stage 27). (A) Larva, dorsal view. Lines on the larval trunk labeled by C–C^III and D–D^III indicate levels of sagittal and transverse sections shown in C–C^III and D–D^III, respectively. CLSM. (B–D^III) Selected sections from complete datasets of serially sectioned larvae. B–B^III frontal sections from the dorsal to ventral sides; C–C^III sagittal sections from the right to left sides; D–D^III transverse sections from the anterior to posterior sides. Light microscopy, Toluidine blue. Enlargements in B^I–B^III, C^I–C^III, and D^I–D^III are the same as in B, C, and D, respectively. Green: ectodermal non-neural tissues; yellow: endodermal tissues; light blue: ectodermal neural tissues; dark blue: mesodermal tissues. (E–E^II) Frontal (E), sagittal (E^I), and transverse (E^II) optic sections of the same larva. CLSM. Enlargement is the same in E–E^II. ant pha: anterior pharynx; epi: epidermis; esp: endostyle primordium; est: endodermal strand; lasp: left atrial siphon primordium; mech: mesenchyme; nc: nerve cord; nd: neurohypophyseal duct; ne: neck; noto: notochord; oc: ocellus; osp: oral siphon primordium; ot: otolith; pha: pharynx; post pha: posterior pharynx; pp: papilla; rasp: right atrial siphon primordium; RTEN: cilium of a rostral trunk epidermal neuron; sv: sensory vesicle; tc: test cell; tf: tail fin; vg: visceral ganglion.