Cell interactions influence the pattern of biomineralization in the Ilyanassa obsoleta (mollusca) embryo

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Abstract
Ilyanassa obsoleta larvae have two calcium carbonate‐containing organs, shell and statocyst, which are derived from five micromere cells (2a, 2c, 2d, 3c, 3d). “Internal shell,” an abnormal, internal calcium carbonate mass, was previously observed when cells which normally induce shell and statocyst were removed. This study utilizes multiple‐cell deletions to examine how these calcium carbonate‐producing precursors control the pattern of biomineralization, whether it is in external shell, statocyst, or internal shell. It was demonstrated that internal shell was solely derived from any of these five cells. However, there was a quantitative difference in the frequency of internal shell production depending upon which cells, as well as how many, are deleted. In general, when external shell or statocyst production was diminished, as the result of removing several of the calcium carbonate‐producing cells, internal shell was deposited instead. The presence of internal shell can best be explained as the result of altered interactions between these five cells after one or more have been deleted. Electron diffraction and transmission electron microscopy show that internal shell differs from normal shell in both structure and crystal morphology and it can also be produced by statocyst precursors. Thus, both the deletion and electron microscopy data support the interpretation that the development of internal shell is controlled by shell‐ and statocyst‐producing cells when the cell communication between these cells is disrupted.