Contents This file contains supplementary data for the article "Genetic parallels in biomineralization of the calcareous sponge Sycon ciliatum and stony corals" Calcarins_alphafold.tar.gz contains the alphafold output data for the structure prediction of selected Calcarins. Orthofinder/ contains proteomes that were used as input for Orthofinder, OrthoFinder result tables, and alignments of Calcarin orthogroups. SciHBWS01all_info.tsv is a tab-separated file with compiled information on the Sycon ciliatum transcriptome used for mapping (NCBI: HBWS00000000.1). Information for each transcript includes corresponding protein IDs and gene IDs, CDS and protein sequence, signal peptide prediction, identified pfam domains, BLAST hits against UniProt, and GO-terms of the best UniProt protein hit. Sycon_ciliatum_gene_predictions/ contains braker gene predictions as gtf-file for the Sycon ciliatum genome (GCA_964019385), using the mapped reads of this study (ERP163002) and predicted proteins from a Sycon ciliatumgenome from Norway (available at http://compagen.unit.oist.jp/datasets.html) as evidence. Sequences of predicted genes and proteins are provided alongside the InterProscan and Pfam annotations for the proteins. Sycon_spicule-peptides.sf3 is a Scaffold-file (.sf3) with information on the proteins identified in the spicule matrix. The Scaffold 5 software is required to open this file (available at https://www.proteomesoftware.com/products/scaffold-5).