Spine elongation in S. purpuratus rudiment. A) single developing adult spine with cross hatches; this spine has 3 cross hatches on the indicated face, but notice that other faces have fewer. B) Spine elongation measured by the average (Avg) and maximum (Max) number of cross hatches in the adult spines of developing S. purpuratus larvae at Stage 8 or later (see Table 2). We detected no significant difference in spine elongation between the first and second 24 hours of development in well plates during the course of the experiment at 14°C. Error bars are one standard error of the mean.