https://orcid.org/0000-0002-2035-1997
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ABSTRACT
Thalassiosira and related taxa i.e. the taxa within Thalassiosirales are among the most abundant and widespread diatoms. The vast majority have one marginal rimoportula, but very few always have two. The knowledge on Thalassiosiroid taxa in Chinese waters is restricted, and to explore the diversity, monoclonal strains were established from southern Chinese coastal waters. Morphological data were based on light and scanning electron microscopy. The D1‒D3 region of the ribosomal large subunit (LSU) and the small subunit (SSU) encoding genes were amplified to address phylogenetic relationships. Based on a combination of morphological characters and molecular analyses, two new species with two marginal rimoportulae were described, Planktoniella pulchra sp. nov. and Thalassiosira tridens sp. nov. Planktoniella pulchra is furthermore characterized by one regular ring of marginal fultoportulae between the valve face and the mantle, as well as dense ribs on the mantle. A narrow circular extension of mucilaginous material surrounds the girdle. In phylogenetic analyses, it clustered within the Planktoniella group. Thalassiosira tridens is unique in having a pronounced external tube of the central fultoportula, as well as long external tubes of the two marginal rimoportulae. Two irregular rings formed by the marginal fultoportulae are present on the mantle, and their external extensions are either open tubes or closed spines. In the SSU and LSU phylogenetic analyses, both taxa constituted their own monophyletic lineage and were well differentiated from allied species. Thalassiosiroid taxa with two marginal rimoportulae were phylogenetically closely related, but did not make up a monophyletic lineage.
Disclosure statement
No potential conflict of interest was reported by the authors.
Supplementary materials
The following supplementary material is accessible via the Supplementary Content tab on the article’s online page at https://doi.org/10.1080/09670262.2022.2029948
Supplementary fig. S1. Phylogenetic analysis inferred from maximum likelihood based on the combined nuclear (D1–D3 region of LSU + SSU) dataset. Only Posterior probabilities from Bayesian inferences (BI) above 0.9 and bootstrap support from maximum likelihood (ML) above 80 are indicated. Stars, circles and triangles represent the Thalassiosiroid species with two marginal rimoportulae, mantle ribs and mucilage extensions, respectively. Outgroups are marked in grey and the remaining was Thalassiosirales taxa.
Supplementary table S1. The genetic distances and the number of differing base pairs of SSU rDNA (in parentheses) among two novel taxa and closely related species.
Supplementary table S2. The genetic distances and the number of differing base pairs of LSU rDNA (in parentheses) among two novel taxa and closely related species.