We seek to develop scalable, environmentally-benign mitigation strategies based on genome-encoded factors used by crown-of-thorns starfish (COTS) in their species-specific communication. When induced into an alarmed state by the presence of a predator, captive COTS secrete compounds that include species-specific proteins. We identified a novel uncharacterized protein in this alarmed exoproteome, and found that it belongs to a family of 11 genes clustered in the COTS Great Barrier Reef genome. This novel gene family encodes secreted proteins with no recognisable protein domains. Members of this family are defined by a set of common motifs, although there are also regions of high sequence divergence. Comparison of Okinawan COTS population and sister-species genomes reveals coding sequence differences between orthologues, suggesting that some members of the family are evolving rapidly. Analysis of gene expression in COTS shows that every member of this family is expressed in spines, which help defend COTS from predators. The presence of these proteins in the alarmed exoproteome, together with their species-specificity, suggests a role in COTS communication. We propose that this novel gene family may provide candidates for COTS-specific mitigation strategies focussed on repelling this starfish away from coral reefs of high economic or environmental value.