We used morphological data for a phylogenetic analysis of the genus Petaloptoctus (Maldanidae: Polychaeta). We found three most parsimonious phylogenetic trees with length = 37, CI= 0.89 and RI= 0.92. The genus Petaloproctus is monophyletic, and is supported by a strongly arched prostomium, pinnate capillary setae, and an anal cup with a reduced dorsal border. Our proposal for the systematisation of the subgroups of Petaloproctus is ((P. tenuis (P. terriculus + P. neoborealis)) (P. ornatus (((P. cirratus + P. dentatus) (P. macrodentatus (P. borealis (P. vallejoi n. sp. + P. socialis)))))). We also regard Nicomachinae as a monophyletic group with the following synapomorphies: prostomium short and arched; nuchal grooves short and curved; cephalic plate lost; anal pore opening on margin of anal plate. Monophyly of Micromaldane and Nicomache was also supported in the analysis. Petaloproctus vallejoi n. sp. has 19 setigerous and one asetigerous pre-anal segment. The prostomium is rounded, forming a keel with curved laterals. Nuchal grooves are short and deep, strongly curved outwards. Each neuropodium has one acicular spine on setigers 1-3. The pygidium has a large ventral border, and a reduced dorsal border. The anus is terminal, and close to the margin of the anal plate, surrounded by divergent folds.
De Assis, J. E., Lindsey Christoffersen, M., & Da Cunha Lana, P. (2010). Phylogenetic analysis of <em>Petaloptoctus</em> (Maldanidae: Polychaeta), with description of a new species from southeastern Brazil. Scientia Marina, 74(1), 111–120. https://doi.org/10.3989/scimar.2010.74n1111