Morphogenesis of Temnopleurus reevesii after cell mass formation through to metamorphosis. (A’,B’,D’,E’,E”,E”’,F’,F”) show higher magnification images in black and white broken squares (A,B,D to F). (A,B) Six-armed larvae 9 days (A) and 11 days (B) after fertilization (ventral view). The cell mass (CM; arrow) has grown and has become attached to the hydrocoel (A). It has changed shape from a CM (A’) to a thin pouch (B’). (C) A posterior pedicellaria of a six-armed larva 11 days after fertilization. (D,E) Six-armed larvae 16 days (D) and 17 days (E) after fertilization: dorsal (D) and ventral (E) views. The epithelium of the CM has thickened (D’), the CM has covered the hydrocoel and the complex has started to form primary podia (E’). Yellowish-green cells become visible in the post-oral (E”) and postero-dorsal arms (Y, a red broken circle) but not in the antero-lateral (E”’) and pre-oral arms. (F,G) Eight-armed larvae 23 days (F) and 27 days (G) after fertilization: dorsal (F) and ventral (G) views. Primary podia are visible, although they are still covered with a thin sheet of the CM (F’). A small process has formed (F”; double arrowheads). Thereafter, the larvae fully developed the adult rudiment (G). (H) A juvenile 31 days after fertilization (dorsal view). (I) A young sea urchin approximately 1.5 years after fertilization (dorsal view). Hy, hydrocoel. Pe, pedicellaria. Scale bars = 100 μm for (A to H) and 1 cm for (I).