Morphology and molecular phylogeny of a new haptorian ciliate, Chaenea mirabilis sp. n., with implications for the evolution of the dorsal brush in haptorians (Ciliophora, Litostomatea).

We discovered a new haptorian ciliate, Chaenea mirabilis sp. n., in brackish water collected near the town of Busan, Korea. Its morphology was studied using standard taxonomical methods and its phylogenetic relationships were assessed by phylogenetic analysis of the 18S rRNA gene. Chaenea mirabilis is distinguished from all congeners by the combination of the following traits: (i) a narrowly bursiform to flask-shaped, 60-100 μm long body; (ii) 11-21 doughnut-shaped or sometimes horseshoe-shaped macronuclear nodules; (iii) two types of extrusomes: type I is rod-shaped and 6-8 μm long, while type II is narrowly to broadly teardrop-shaped and only 1.5-2 μm long; (iv) highly refractive special granules tightly arranged between the first and second brush row, forming a conspicuous bulge; and (v) 12-13 somatic kineties. In the 18S rRNA gene phylogeny, C. mirabilis clustered with full support with other congeners. However, there was no statistical support for classification of Chaenea into the families Fuscheriidae, Acropisthiidae, or Trachelophyllidae, but a sister relationship with the Lacrymariidae could not be excluded. Therefore, we establish a new family, Chaeneidae, within the order Lacrymariida. This affiliation is strongly corroborated by the distinctly subapical dorsal brush bearing cilium-like bristles.