This picture is of a different experimental urchin. This is a dorsal view which is why the juvenile rudiment is above the stomach rather than below it. Also, this picture was taken with a 4x magnification lens while the previous were taken with a 10x. (The larvae were approximately the same size). The larval arms aren't quite as straight as on the previous pictures - maybe it was waving to the camera. However, what is interesting about this larva is the size of the juvenile rudiment. It's about the same size, if not larger, than the stomach. It is not uncommon for larvae of the same age to have rudiments of different sizes. Despite the fact that our Embryology class is ending on June 7th, I will continue to rear these larvae. I hope my next pictures are an illustration of urchin metamorphosis!
See also my earlier posts on blastomere separations: Part 1 Part 2