Osborn, Karen J.; Rouse, Greg W. 2010. Phylogenetics of Acrocirridae and Flabelligeridae (Cirratuliformia, Annelida). Zoologica Scripta 40: 204–219.

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When seven deep-sea, swimming cirratuliforms were recently discovered, the need for a thorough phylogenetic hypothesis for Cirratuliformia was clear. Here, we provide a robust phylogenetic hypothesis for the relationships within Acrocirridae and increase the taxon sampling and resolution within Flabelligeridae based on both molecular (18S, 28S, 16S, COI and CytB) and morphological data. Data partitions were analyzed separately and in combination. Acrocirridae and Flabelligeridae were reciprocally monophyletic sister groups when rooted by cirratulids. The seven recently discovered species form a clade within Acrocirridae and will be designated as four genera based on phylogenetic relationships and apomorphies. A revised diagnosis is provided for Swima, restricting the genus to three species distinguished by a thick gelatinous sheath, transparent body, simple nuchal organs, a single medial subulate branchia, and four pair of small segmental branchiae modified as elliptical, bioluminescent sacs. Helmetophorus and Chauvinelia are maintained as separate genera based on morphological differences. Evidence for flabelligerid branchiae being segmental is provided, the papillae on segment two of most acrocirrids is confirmed to be the nephridiopores, and scanning electron microscopy is used to examine acrocirrid spinous chaetae in comparison with flabelligerid segmented chaetae.

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