**5. Conclusions**

This study provides the first characterization and quantification of the association between the cryptic hydrozoan *Nemalecium lighti* and the demosponge community within the coral reef systems of Bonaire. This hydrozoan has been found to be a generalist symbiont of different genera of sponge along the west coast of Bonaire. Even though the differences in the prevalence of occurrence of the associations were not significantly important with regards to the depth, future investigations extending into the deeper parts of the reef, including mesophotic depths, may be important to better define the role of depth in this association. However, the dimension of the host resulted in influencing the prevalence of association, with a large tubular sponge found to be the preferred host for *N. lighti*. Moreover, the taxon-specific prevalence revealed that the genus most involved in the association with *N. lighti* was *Aplysina,* with an extremely higher prevalence value compared to the other genera recorded. This may be associated with the production of brominated alkaloid metabolites that serve as antimicrobial and biofouling as well as chemical protection from predators. Additional studies are needed to better understand the implications of this preference and what the main biological and ecological reasons for these results are. Overall, this study improves our understanding of the cryptofauna diversity of coral reef associations in Bonaire.

**Author Contributions:** Conceptualization, J.G. and S.M.; validation, J.E.G.-H., S.M. and D.S.; formal analysis, J.G. and A.M.; investigation, A.M. and F.V.; writing—original draft preparation, J.G.; writing—review and editing, S.M., J.E.G.-H. and D.S.; supervision, S.M., F.V. and P.G. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Reef Renewal Bonaire Foundation for the logistic support provided. AM is grateful to Giorgia Ferrari and Camilla Rinaldi for the unique help during the field activities.

**Conflicts of Interest:** The authors declare no conflict of interest.
