Morphology, morphogenesis, and multigene phylogeny of Stichotricha koreana sp. nov. (Alveolata, Ciliophora, Hypotricha): taxonomic implications for the family Chaetospiridae Jankowski in Small & Lynn, 1985

The morphology, morphogenesis, and multi-gene phylogeny of a new hypotrich, Stichotricha koreana sp. nov., from a temporary pond in Gangneung-si, South Korea, were investigated. The new species inhabits a gelatinous lorica that is often branched, forming a colony. Diagnostic features include two frontal cirri, one buccal cirrus, a short parabuccal row, two frontoventral cirral rows, a single marginal row on each side, and three dorsal kineties, each with a caudal cirrus.

The frontoventral rows, marginal rows, and dorsal kineties spiral by half to one turn around the long body axis. Detailed morphogenesis is documented in the genus for the first time: the oral primordium arises close to the left frontoventral row; the parental adoral zone is fully retained; frontoventral rows, both marginal rows, and all dorsal kineties develop at two levels via within-row anlagen formation; and the parabuccal row originates from the oral primordium.

Phylogenetic analyses of 18 S rDNA place Stichotricha koreana sp. nov. within Chaetospiridae, forming a sister group to members of the family Gonostomatidae and the core urostylids. A concatenated rDNA gene dataset shows that Chaetospiridae is sister to hypotrichs with gonostomatid oral apparatus. These data refine the diagnosis of Chaetospiridae and confirm the generic assignment of S. koreana sp. nov.