Preliminary study on the systematic relationships of Sabellinae (Polychaeta, Sabellidae), based on the C1 domain of the 28S rDNA, with discussion of reproductive features

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Abstract
Systematic relationships of some taxa within the subfamily Sabellinae (Polychaeta: Sabellidae) based on the sequence of the Cl domain of the 28S rDNA coding gene are assessed, and the cladogram obtained are discussed in the light of some reproductive and morphological features. Sixteen different species belonging to 12 genera, were analysed. The cladograms, obtained with different methods (distance UPGMA, maximum parsimony and maximum likelihood) are consistent, except for the ambiguous position of Amphiglena. Three main groups of species, showing similarity in reproductive features and sperm morphology (acro‐some structure) were identified, the taxa included in group A (Myxicola, Chone, and Euchone) show different reproductive strategies and sperm morphology with elongated nucleus, rounded mitochondria and pointed acrosome. Group B contains large sized free‐spawning forms, generally with an ect‐aquasperm type of spermatozoa (Bispira, Sabella, Sabellastarte, and Branchiomma). Taxa included in group C (Eudistylia, Schizobranchia, Pseudopotamilla, Perkinsiana and Demonax) show high variability in sperm morphology, but with a peculiar acrosome structure. The position of Amphiglena is variable, being closer to group A in the distance and maximum parsimony trees, and to group C in the maximum likelihood tree. From previous morpho‐functional analyses, the genera clustering in group A represent the most plesiomorphic taxa, while those in group C contain the most apomorphic ones. Although the general patterns obtained with this preliminary molecular analysis are highly consistent with those arising from the morpho‐functional characters available form the literature, the resolution among genera and species within each of the main groups identified is not consistent, and some of the polytomies and phylogenetic problems among taxa still remain unresolved.

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