Whole mount in situ hybridisation in N. vectensis (a-v) and schematic summaries of expression patterns (w-z). (a-j) Cryo-sections of juvenile septal filaments (‘sep fil’). (k-v) Optical sections of mid-planula larvae (‘mp’, k-r, 2 days p.f.) or late planula larvae (‘lp’, s-v, 4 days p.f.). All planula larvae are viewed laterally, and oriented with the mouth opening pointing towards the bottom.