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Figure 2


Fig. 2. Development of the embryonic skeleton of euechinoid sea urchins. (A) A living sea urchin embryo (Lytechinus variegatus) at the late gastrula stage. The PMCs adopt a characteristic ring-like pattern within the blastocoel and secrete two skeletal rudiments (arrowheads). (B) A living pluteus larva (L. variegatus) viewed with partially crossed polarizers (image courtesy of Dr Rachel Fink, Mount Holyoke College). The mineralized skeleton (arrowhead) is birefringent. (C) Scanning electron micrograph of the late embryonic skeleton (Dendraster excentricus), with all cellular material removed.