Taxonomy and phylogeny of two new species of Frontoniidae (Ciliophora, Peniculida) isolated from black soil farmland in northeastern China

This study examined the morphology and infraciliature of two soil ciliates, Protofrontonia mudanjiangensis sp. nov. and Frontonia legumen sp. nov., collected from farmland in Mudanjiang, Heilongjiang Province, Northeastern China, using live observation and silver carbonate impregnation. Protofrontonia mudanjiangensis sp. nov. is characterized by a body elliptical in outline, measuring 70–85 × 35–45 μm in vivo, 43–50 somatic kineties, three vestibular kineties with the second one interrupted, three to five postoral kineties, four kinetosomal rows in peniculi 1 and 2, two rows in peniculus 3, a long ellipsoidal macronucleus, and one contractile vacuole located about two-fifths from the posterior end on the ventral side, with one vacuole pore on the dorsal side. Frontonia legumen sp. nov. has an elliptical body of 55–75 × 35–50 μm in vivo, 37–45 somatic kineties, three vestibular kineties, four to five postoral kineties, three rows in peniculus 1, four rows in peniculus 2, a single row in peniculus 3, one macronucleus and two micronuclei, and one contractile vacuole located about two-fifths from the posterior pole on the ventral side, with two or three vacuole pores on the dorsal side. Phylogenetic analyses based on SSU rDNA sequences showed that P. mudanjiangensis sp. nov. clustered within the core clade of Protofrontonia , and F. legumen sp. nov. grouped with the genus Frontonia . Their distinct morphology and molecular divergence support their status as new species, enriching knowledge of the morphological diversity and molecular phylogeny of Frontoniidae.