A new marine monoraphid diatom species, Planothidium pseudolinkeisp. nov., is described from the coast of Guangxi, China. The detailed morphology of this epipsammic diatom is studied by using both light and scanning electron microscopy. P. pseudolinkei differs from congeners by a combination of morphological features including capitate apices, multiseriate striae, a small central area on the raphe valve and an oblong sinus on the rapheless valve. Ecological preferences of Planothidium are also briefly discussed.

Two new diatom species belonging to the genus Gomphonemopsis are described, Gomphonemopsis nanasp. nov. and Gomphonemopsis gaoisp. nov. These two species were compared in detail with congeners. Gomphonemopsis nana is distinguished by its high stria density and small size. This species was found so far to be epiphytic only on the eelgrass collected from Qingdao Bay (Yellow Sea). Gomphonemopsis gaoi is characterized by its isopolar valves, simple proximal raphe endings and acutely rounded apices. This taxon was separated from the exoskeleton of marine copepods sampled from the Futian Mangrove Nature Reserve (South China Sea). In addition, two new combinations, Gomphonemopsis oahuensis (Hustedt) Lang Li, Yuhang Li & Changping Chen, comb. nov. and Gomphonemopsis platypus (Østrup) Lang Li, Yuhang Li & Junxiang Lai, comb. nov. are proposed. This study increases the records and knowledge of Gomphonemopsis along the coast of China.

Epiphytes significantly contribute to the overall primary productivity of seagrass beds. Among them, diatoms are the most diverse and important component of the epiphytic community in seagrass beds. However, studies on this group of diatoms are still limited in China. In this research, we investigated the epiphytic diatoms on Zostera marina Linnaeus from Qingdao Bay on the western coast of the Yellow Sea. A total of 112 taxa belonging to 31 families and 57 genera were morphologically identified, of which 16 taxa were newly recorded in China. Each taxon was illustrated with corresponding light micrographs. The most common genera were Navicula Bory with 12 taxa, Amphora (Ehrenberg) Kützing with 10 taxa, and Nitzschia Hassall with 10 taxa. Notably, species of Cocconeis Ehrenberg were ubiquitous and found in every sample. Based on our observations, the sediment is proposed as a likely source of these epiphytic communities. None of the newly recorded diatoms had been previously reported as epiphytes on seagrasses. Our results improve the understanding of species diversity and distribution of seagrass epiphytic diatoms along the coasts of China.