New insights into the phylogeny of the Acantharea based on SSU rRNA gene sequencing

The phylogeny of the Acantharea was examined using small-subunit ribosomal RNA (SSU rRNA) gene sequence analysis of representatives from the Symphyacanthida, Chaunacanthida and the Arthracanthida. Our previous studies showed that Acantharea form a monophyletic group branching as an independent protist lineage among crown groups but not directly related to any of them. The results from this more in-depth molecular analysis of the branching patterns within the Acantharea revealed a phylogeny which is not entirely consistent with morphology-based phylogenies. In particular, the phylogenetic placement of Haliommatidium sp. was in disagreement with its current placement among the Symphyacanthida based on morphological features. Haliommatidium sp. clustered with members of the order Arthracanthida in molecular analyses described herein. In retrospect, Haliommatidium sp. shares several morphological features with the Arthracanthida which support these molecular results.