Sea urchins were tagged with a fluorescent marker, released into tidepools, and collected 1 year later. We quantified the position of the fluorescent mark relative to subsequent growth bands. The banding pattern in ossicles seriously underestimates age in S. droebachiensis and population parameters inferred from these growth lines are biased. Before using the growth-band aging method in other echinoids, it must be demonstrated that 1 band is added annually for all sizes in a population under field conditions. The ciliary band of the auricularia larva runs along a series of ridges that project from the sides of the body.
Fragmentation results from a loss of ciliary band cells from the zones between the ridges.
The remaining fragments then reorient, elongate, and fuse to form the 5 circumferential bands of the doliolaria. The fate of the band cells lost during this process could not be determined with certainty, but they disappear after being sequestered beneath the epithelium for a time, probably through histolysis. Cell counts indicate that significant numbers of cells are also lost from the ridges. Normal swimming ceases just before transformation begins, probably because the nerve supply to all or parts of the band is disrupted, and this may play a role in initiating morphogenesis. 1 North, Ft.