Exploring the diversity of Brachonella: Morphological and molecular analysis with the discovery of a new species, Brachonella tenuicauda nov. spec. (Ciliophora, Armophorea, Metopida)

Abstract

Recently, the interest in studying anaerobic ciliates, particularly armophorean ciliates of the family Metopidae, has increased. The genus Brachonella, a member of this family, currently comprises eight species. However, only four of them have been comprehensively described, with B. contorta, the type species of Brachonella, being the subject of extensive global distribution analyses. This study presents a comprehensive morphological and molecular phylogenetic analysis of B. tenuicauda nov. spec., B. elongata, and B. pulchra. Brachonella tenuicauda is characterized by a tail-like posterior body end and by clusters of two to four dikinetids in the preoral dome kineties. Brachonella elongata is identified by its slender, elongated body without posterior constriction, whereas B. pulchra shows a broadly ellipsoidal to nearly obovoid body. Korean populations of B. pulchra and B. tenuicauda exhibit a diplostichomonad paroral membrane, a feature not previously documented for this genus. Phylogenetic analysis of 18S rDNA sequences indicates non-monophyly of the family Metopidae. Conversely, the genus Brachonella is depicted as monophyletic with full support, confirming its molecular distinctness from other metopid genera.