Development of Temnopleurus toreumaticus from the prism to the six-armed larval stage. Light (A,E to L) and scanning electron micrographs (B to D) showing the initial left-right asymmetry of the elongation of the primary pore canal (PPC) and the initiation of the adult rudiment formation from the cell mass (CM). (A,B) Prisms 23 h after fertilization (dorsal view). The PPCs have formed bilaterally; the hydropores (arrowheads) are located bilaterally. (C,D) Prisms 26 h after fertilization: oral (C) and left lateral (D, the left lateral ectoderm was removed by cellophane tape before coating) views. Two cells have started to invaginate (arrow). (E) A two-armed larva with the CM 34 h after fertilization (aboral view). (F) A four-armed larva with a hydropore only on the left dorsal side 3 days after fertilization (dorsal view) (G) A four-armed larva 6 days after fertilization (ventral view). (H) A six-armed larva 10 days after fertilization (dorsal view). The insert shows higher magnification image in a black broken square. (I) A six-armed larva 15 days after fertilization (ventral view). The CM has attached to the hydrocoel. (J,K) Six-armed larvae 20 days after fertilization: ventral (J) and dorsal (K) views. The CM has budded a small process (double arrowheads). (L) A six-armed larva with a small process 22 days after fertilization (ventral view). Hy, hydrocoel; Y, yellowish-green cells (a red broken circle). Scale bar = 50 μm for (A to D,F,K), 100 μm for (E,G to J,L).