Macroid Formation in <i>Salmacina stellaebayensis</i> n. sp. From Mauritania's Baie de l'Étoile With New Insights on Mitogenome Evolution in Serpulidae (Annelida)

Knowledge of serpulid diversity along the West African coast remains scarce. Here we describe <i>Salmacina stellaebayensis</i> n. sp. from the Baie de l'Étoile, Mauritania, a new macroid-former generating striking star-shaped pseudo-colonies. Combining classical morphology with genomic data, we provide the first complete mitochondrial genome for the genus <i>Salmacina</i> and recover additional nuclear markers to clarify its phylogenetic placement within Serpulidae. <i>Filograna</i> and <i>Salmacina</i> form a taxonomically challenging group with uncertain generic boundaries. While additional data from operculate <i>Filograna</i> are needed, this study provides a valuable baseline and much-needed molecular framework for future revisions. Comparative analyses of 17 serpulid mitogenomes reveal extensive variation in gene order, supporting the view that mitogenome plasticity represents a family-level feature of Serpulidae. The new species also exhibits frequent asexual reproduction by budding and anterior regeneration, extending known life-history diversity in the group. Together, these findings enhance our understanding of serpulid systematics, life history, and mitochondrial evolution, underscoring the value of integrative approaches in uncovering annelid biodiversity from underexplored regions.