Tentacle transcriptomics identifies candidate chemosensory receptors in the gray field slug Deroceras reticulatum

Chemosensation is essential for foraging, predator avoidance, and reproductive behavior in terrestrial gastropods. The gray field slug ( Deroceras reticulatum ) is a globally important agricultural pest, yet the peripheral molecular mechanisms driving its chemosensory behavior remain poorly understood. Here, we generated and analyzed de novo transcriptomes of the upper posterior tentacles (PT) and lower anterior tentacles (AT), using non-sensory mantle tissue (MT) as a comparative baseline. Illumina sequencing and de novo assembly yielded 142,526 transcripts, of which 28,310 were functionally annotated. Tissue distribution and differential expression analyses revealed marked molecular specialization between the two tentacle pairs. PT-enriched transcripts were associated with aerial olfaction and photoreception, including neural signaling components, retinal-associated genes, and G protein-coupled receptors (GPCRs), whereas AT-enriched transcripts were associated with contact chemoreception and substrate-associated sensing, with enrichment of structural remodeling components, acetylcholine receptors, and metabolic enzymes. Targeted gene-family mining showed that GPCRs dominated the annotated chemosensory repertoire. A multistep bioinformatic filtering pipeline identified 67 PT-enriched and 38 AT-enriched candidate chemosensory GPCRs, including numerous uncharacterized or orphan receptors. Non-GPCR candidate families included ionotropic glutamate receptors, degenerin/amiloride-sensitive sodium channels, lipocalins, and Niemann-Pick type C2 proteins. qRT-PCR analysis of 17 high-priority candidate GPCRs largely supported the RNA-Seq expression patterns. Together, these tissue-specific profiles provide a molecular resource for understanding slug chemosensory biology and for prioritizing candidate targets for future behavior-based or molecular pest-management strategies.