DYNAMICS AND GROWTH-PATTERNS OF CALCAREOUS SPONGE SPICULES

Morphogenesis of different-shaped biogenic crystals presents one of th e important biomineralization problems. Growth of various calcitic spi cules from Sycon sp. have been studied by using calcein marking. We fo und that spicule production is dependent on various conditions such as location in the sponge body and illumination, whereas the calcificati on rate by the spicule-forming cells is constant. Morphological, cryst allographic and fluorescence analyses have enabled the investigation o f the growth patterns of the different spicule types. We suggest that different mechanisms are involved in the growth of various spicule typ es. Triradiate spicules are deposited from the centre towards the rays . Crystallographically different rays of the triradiates differ in the dynamics of formation as well. Slender monaxon spicules are deposited very fast (more than 65 mu m/h). Two calcification sites are involved in the secretion of curved monaxon spicules. These spicules grow unid irectionally from one extremity at a rate of 12.0 mu m/h, and are thic kened at some distance from the nucleation site. Possible mechanisms t hat may account for the observed growth patterns are discussed.