Spine regeneration in larvae of the crab, Rhithropanopeus harrisii

Dorsal spines were removed from intermolt first instar larvae of Rhithropanopeus harrisii. The wound was immediately closed by hemocytemediated clot formation. Epidermal cells from regions adjacent to the spine then formed a continuous, single-cell-thick layer beneath the clot. During premolt of the first instar, the distal cells formed a new spine tip by apical extensions. Regenerating spines underwent enhanced growth during the first two instars; this resulted in a normal-sized spine by the third instar. Determination of cell density in regenerating spines indicated that the enhanced growth during reeneration was due to increased cell division during the first two instars. Spine regeneration had no effect on duration of the molt cycle, onset of premolt, or metamorphosis.