Insights into adhesive and neuronal cell populations of the chaetognath Spadella cephaloptera using a single-nuclei transcriptomic atlas and genomic resources

To cope with extreme environmental conditions diverse marine species have developed mechanisms that allow them to permanently or temporarily attach to substrates. In the intertidal zone of marine habitats, where tidal ranges and currents may drift organisms away from their habitat, temporary adhesive systems such as the one inherent the arrow worm Spadella cephaloptera (Chaetognatha) constitute an essential trait for the survival of this taxon. The underlying molecular mechanism of this system has not been described yet, and the existing morphological information is limited to adults. Furthermore, a relationship between the nervous system and the attachment in S. cephaloptera remains to be demonstrated. In this study, single-nuclei sequencing of S. cephaloptera hatchlings was performed, using as a reference a newly sequenced and assembled genome to identify the transcriptomic profiles of the cells mediating attachment, neuronal populations, and the main cell types of chaetognath hatchlings. Our findings, supported by previous studies, suggest that the chaetognath adhesive system evolved convergently to those of other other metazoans. Moreover, diverse cell types were identified in the ventral nerve center and multiple ciliated cell types previously described from anatomical observations were validated. Ongoing in-depth investigation of these data, together with datasets from other developmental stages, will provide further insights into the evolutionary origins of the unique chaetognath body plan.