New records of the colonial chrysophyte Urostipulosphaeraarticulata (Chrysophyceae, Ochromonadales) in China.

Background: The genus Urostipulosphera was established in 2019. Its morphological characteristics are similar to Uroglena and Uroglenopsis, but it differs from both. This genus connects individual cells into communities through a dichotomous branching structure, which distinguishes it from Uroglena and Uroglenopsis. Although there are nine species in this genus, molecular data are available for only four species. Molecular data and species distribution records for Urostipulosphaera are severely lacking. Species of this genus have been recorded in a few locations in Europe and North America.

New information: We identified three samples that were discovered in Shanxi Province, China, based on morphological characteristics and molecular phylogenetic analysis. Results of the polygenic phylogenetic tree, based on SSU, rbcL and ITS sequences, showed that the three samples were clustered with Urostipulosphaeraarticulata U5-5 from Czechia, with a high support rate of 100/1.00. Morphological observations further supported this result. Therefore, the three samples were identified as Urostipulosphaeraarticulata. This is the first report in China and enriches the geographic diversity of this species. Moreover, we found the long flagellum with mastigonemes under the scanning electron microscope complementing the description of the morphological characteristics of this species. The ITS2 secondary structure of the specimens differed from that of Urostipulosphaeraarticulata U5-5, which exhibited a loop and five-arm structure. A Bayesian relaxed clock analysis indicated that the genus Urostipulosphaera originated in the Early Cretaceous, approximately 109.85 million years ago (Ma) and diverged into two clades around 79.81 Ma.