P. L. Clode, A. T. Marshall. 2003 Calcium associated with a fibrillar organic matrix in the scleractinian coral Galaxea fascicularis. Protoplasma Volume 220, Issue 3-4, pp 153-161

I think that this paper and the references within give a good explanation of how the calcification process in corals works.

You might also be interested in the process by which marine algae produce calcium-based structures.

Hello Amaravadi, I would look at papers on the gene galaxin. It encodes a skeletal organic matrix protein, but I do not know whether it is a protein hormone, or even if this is known.  This paper includes some key references on galaxin: 

Differential expression of three galaxin-related genes during settlement and metamorphosis in the scleractinian coral Acropora millepora

http://www.biomedcentral.com/1471-2148/9/178#B8

Here is another paper that you may find interesting: 

Proteomic analysis of skeletal organic matrix from the stony coral Stylophora pistillata

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3593878/

If you are interested in comparative sequence data, I would also look at the different RNA-seq studies that were published in recent years on corals, such as the papers by Daniel Barshis et al. 

Cheers, eric

Thanks Eric. Thank you very much.