Ultrastructural investigation of spicule formation in the gorgonian Leptogorgia virgulata (Lamarck) (Coelenterata: Gorgonacea).

Ultrastructural examination of original and regenerated branch tips of the gorgonian Leptogorgia virgulata reveals that spicule formation begins with the aggregation of Scleroblasts in the mesoglea. Calcite crystal deposition occurs within a Golgi vacuole containing organic matrix. Vacuole size increases while matrix incorporation and subsequent crystal growth continue, filling the vacuole. At approximately this time, the scleroblasts dissociate and "wart" formation begins. Further spicule growth stretches the cell into a thin envelope. Fusion of vacuole and plasma membrane followed by breach formation during spicule growth, as well as scleroblast atrophy or migration from mature spicules, result in the transition of the spicule from the intracellular to the extracellular environment. The results also reveal aborted spicules and digestive bodies, implying possible relationships among calcification, detoxification, and waste management.