Egg capsule mineralization via vaterite transportation in the invasive apple snail Pomacea canaliculata

The invasive apple snail Pomacea canaliculata utilizes calcified egg capsules as a key adaptation for terrestrial reproduction; however, the biomineralization mechanisms underlying capsule formation remain poorly understood. In this study, we found that vaterite, a rare calcium carbonate polymorph, was deposited in the egg capsule through a unique transport and assembly process. We demonstrated that calcium carbonate nanoparticles (several hundreds of nanometers in diameter) were initially stored in the egg yolk and subsequently transported to the capsule surface, where they formed a protective vaterite layer (around 10 μm). Proteomic and transcriptomic analyses identified a specialized organic matrix. This matrix contains chitin-binding proteins (CBPs), sulfatases, and calcium-binding proteins, which act collectively stabilize vaterite and inhibit calcite formation. Phylogenetic analysis suggested CBPs represent a group of evolutionarily conserved yet functionally versatile secretory proteins, distinct from shell-specific proteins like Pif, highlighting the snail's ability to repurpose existing genes for novel mineralization. Furthermore, gland-specific transcriptomics revealed upregulated pathways in mineral absorption and glycosaminoglycan biosynthesis, underscoring the coordinated roles of the albumen and capsule glands in matrix production. These findings not only elucidate a unique biomineralization strategy in the apple snail but also identify potential molecular targets for disrupting capsule formation, offering new avenues for controlling this globally invasive species.