Untangling green filaments: Two new species of <i>Chaetomorpha</i> and phylogenetic analysis of <i>Pseudorhizoclonium</i> from the Southwestern Atlantic

SUMMARY Chaetomorpha , Pseudorhizoclonium , and Rhizoclonium have been reported from the Brazilian coast and oceanic islands; however, molecular data are currently restricted to Pseudorhizoclonium . We aimed to investigate the diversity of Chaetomorpha and Pseudorhizoclonium in the Southwestern Atlantic based on LSU and SSU sequences, as well as morphological data. Samples were collected from the Brazilian coast (Alagoas State) and along three oceanic archipelagos (São Pedro e São Paulo, Fernando de Noronha, and Trindade). Our data confirmed the occurrence of Chaetomorpha antennina and Pseudorhizoclonium mangroviorum , extending the known morphological characterization of both species and expanding the documented distribution range of P. mangroviorum to include northeastern Brazil. Additionally, based on newly generated phylogenetic data, we propose the description of Chaetomorpha costacoralla sp. nov. and Chaetomorpha insularis sp. nov. Morphologically, Ch costacoralla is similar to Chaetomorpha gracilis and is currently restricted to the northeastern Brazilian coast. On the other hand, Ch. insularis is a microfilamentous taxon found only as an epiphyte on other macroalgae in Fernando de Noronha. Our data suggest that Chaetomorpha diversity along the Brazilian coast is currently underestimated, as seen by the description of two new species and the identification of a potential novel species within the Chaetomorpha spiralis complex.