Álvarez-Campos, Patricia; Lattig, Patricia; Turon, Marta; Martín, Guillermo San; Buckley, David; Britayev, Temir A.; Martin, Daniel & Machordom, Annie. (2025). Evolution of Haplosyllis (Syllidae, Annelida) With Emphasis on the Indo-Pacific Region and the djiboutiensis Species Complex. Zoologica Scripta. 54(5): 684-707.
Annelidabase, open access, registered nomenclatural act in ZooBank not yet viewable. Published in print journal 26/8/2025
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Haplosyllis is a worldwide distributed genus of marine annelids, commonly associated with other invertebrates. Its characteristic simple bidentate chaetae have often led to mistakes in estimating the real diversity of the genus. Currently, Haplosyllis includes 38 species, nearly half of which inhabit the Indo-West Pacific (IPW). Nevertheless, this number might be much higher given that some of the most common species in this area, such as H. djiboutiensis, have been proposed to constitute complexes of several species. To investigate the diversity and evolutionary history of Haplosyllis in the IWP, we examined the morphology of 158 specimens from this area. In addition, we inferred phylogenies through Maximum Likelihood and Bayesian analyses using a multilocus molecular dataset from all Haplosyllis specimens and related genera. Our results indicate that: (1) Haplosyllis, Haplosyllides, and Parahaplosyllis are non-sister clades, (2) Haplosyllis is a polyphyletic genus, as Branchiosyllis, Alcyonosyllis, and Megasyllis are nested within it, and (3) there are four main well-supported clades including species of Haplosyllis that can be considered as different genera. However, robust morphological synapomorphies were only found for two of them, which we are describing as Haplosyllis sensu stricto and Paralcyonosyllis gen. nov. In addition, our detailed morphological study of the H. djiboutiensis complex, combined with a coalescence-based species delimitation analysis, confirmed that it is a complex of both cryptic and pseudo-cryptic complexes, with at least three distinct lineages/species.
