Fig. 4. LR positioning of the hydropore canal in the left half H. pulcherrimus larvae dissected in the mid-late gastrula stage. Two left lateral views of a four-armed pluteus, with the oral side (anterior side) to the left of the figures are shown. (A) A larva with the focal plane on the left coelomic sac (arrow). No hydrocoel has developed from the left coelomic sac. (B) The same larva as shown in A, with the focal plane on the right coelomic sac. A hydrocoel (arrow) is seen developing from the right coelomic sac. Scale bar: 100 µm.