BLOSUM62 cluster map showing sequence similarity of echinoderm SS1-type and SS2-type peptide precursors with SS/ASTC-type peptide precursors in other taxa. Nodes are labeled with phylum-specific colors, as shown in the key, and connections represent BLAST relationships with a P value >1e-2. Vertebrate precursors of UII, URP-type peptides, and MCH, which are structurally and evolutionarily related to SS/ASTC-type neuropeptides, were also included for comparison. Note that echinoderm SS1-type peptide precursors only have connections with protostome ASTC-type precursors, whereas echinoderm SS2-type peptide precursors only have connections with vertebrate SS/CST-type precursors. This indicates that echinoderm SS1-type peptide precursors are orthologs of protostome ASTC-type peptide precursors and that echinoderm SS2-type peptide precursors are orthologs of vertebrate SS/CST-type precursors. The A. rubens SS1 precursor (ArSSP1) and SS2 precursor (ArSSP2) are boxed. The accession numbers or references for sequences of the precursors included in this figure are listed in SI Appendix, Table S2.